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GEO-PHYSICAL SCIENCE 2011-2012 Mr. Sacks GEOPHYSICAL SCIENCE POLICIES & PROCEDURES Schools exist primarily for the purpose of learning. To achieve that goal, we both must do our jobs. I. MY JOB INCLUDES: 1) Arriving to class on time. 2) Being prepared with a clear lesson plan and a thorough knowledge of the material. 3) Being ready to work when the bell rings. 4) Providing all materials that I’m responsible for. 5) Giving homework and exams which reflect and utilize the concepts presented. 6) Providing current and accurate assessments of your performance. 7) Informing you of short-term assignments and their due dates. II. YOUR JOB INCLUDES: 1) Arriving to class on time. 2) Being prepared everyday with notebook paper, at least one #2 pencil with eraser, graph paper (if necessary), colored pencils if needed, and any other materials accumulated during the course which may be necessary to perform the assigned work. 3) Being ready to work when the bell rings. This includes being in your designated seat and starting any warm-up activities. 4) Completing the homework on time and as instructed. 5) Asking questions if you don’t understand something. 6) Taking the necessary steps to legitimately maximize your performance in this class. Examples would include using effective study techniques, coming in for extra help when appropriate, doing the homework, taking good notes, taking advantage of Extra Credit opportunities, etc. 7) Being aware of assignments and their due dates. 8) PAYING ATTENTION!! III. DISCIPLINE AND CLASS CONDUCT No student will be allowed to impede the learning process. It prevents me from doing my job and the other students from doing theirs. I have found that using the guideline “impeding the learning process” is a better way to determine what an offense is than trying to anticipate and list every possible infraction. ATTENDANCE: A student is considered tardy if not completely seated at his assigned desk before the bell stops ringing. Notice how this sharply contrasts with students’ wishful interpretations like “But I was in the room!”, or “But I was just a little late”, or “But my books were on the desk. I just had to talk to my girlfriend for a second.” or any other excuse that starts with the word “But”. FOOD FOR THOUGHT: This is a classroom, not a cafeteria, so food doesn’t belong here. It attracts bugs and rodents, is not consistent with our purpose here, and is unsafe given the fact that we conduct chemical labs in the room. Water in a plastic container with a screw cap is welcome. But food (including gum) and other beverages must be consumed outside the room. Repeat violators will become intimate with that which they love so well. This love will be demonstrated for one hour after school by sweeping up crumbs and scraping gum off desks. IV. GRADING EXAMS: There are quizzes (50 pts.), tests (100 pts.), and a cumulative Semester Final Exam which is worth 30% of the class grade. There are no mid-terms or pop quizzes. During any exam, you must be entirely self-sufficient during the entire period. That means no student shall communicate with, nor receive nor supply information or materials of any kind, from another student - NO EXCEPTIONS! If you have a question, if you can’t read the board or the exam, if you need to borrow something, ask me, no one else. LABS: These are a good way to apply the stuff we learn, so they will be conducted as often as equipment and time allow. The point value of labs varies, depending on their complexity and length. The lab equipment is safe when used as instructed. However if materials are abused, then both people and property are put at risk. Necessary safety lectures will be given before all labs; therefore anyone deliberately endangering persons or property will be withdrawn from that lab and receive a zero. Continued abuse will result in expulsion from the course. There are no plant or animal dissections in this class. CLASS PARTICIPATION: Pretty self-explanatory. Ask questions, get involved in the discussions, notice how the world around you is a giant, living lab. You have the right to learn. You have the right to remain silent. You also have the right not to learn, assuming that you want to stay in high school for 7 years and then get a job as a toothpick sharpener. But one right that you do not have is the prevention of anyone else from learning. Consequently, actions which impede the learning process are unacceptable, and responses from the subtle to the severe will result. HOMEWORK: “Daily” assignments will generally be the rule (this class does not meet every day). But I also try to avoid homework on holidays and vacations, and never give an assignment the day before an exam. At the start of each week, you will be given a syllabus of the week’s assignments. Each morning, your notes and homework will be assessed and your progress will be indicated on the syllabus. On the day of the exam, your syllabus will be collected. MAKE-UP WORK: Work missed due to a suspension will not be accepted. Late homework is accepted only for excused absences. The amount of time you get to make it up is determined by how long you were out. For example, if you missed 3 school days, then you have 3 school days to make it up. Make-up labs and exams are typically conducted after school. If that conflicts with your personal schedule (job, medical appointment, etc.), let me know before that day arrives so that alternate arrangements can be made. Don’t just go AWOL on the make-up day. It is to your advantage to take the original exam if possible because repeat tests are always harder than the original. Consequently, if you know that you’re going to be gone on an exam day, tell me at least three days in advance so I can let you take the original one before you leave. GRADE COMPONENTS: Exam Grades: 80% - 100% = A 70% - 79% = B 60% - 69% = C 50% - 59% = D Quarter Grade: Exams: 50% Lab Reports: 20% Homework & Class notes: 30% Semester Grade: Quarter 1: 35% Quarter 2: 35% Final Exam: 30% V. LIFE IN GENERAL You (yes, you) are the paramount factor in how well you do in this class (or any other class for that matter). You are responsible for your own actions and their consequences (which includes grades). If you get behind in the work, if you don’t understand something, if you need some extra help, you have to let me know. (If I could read minds, I’d be at a poker table right now.) By implementing these guidelines, I’ll be able to teach more efficiently and you might even find this class to be interesting (imagine that!) Mr. Peter Sacks Science Department IRVINE HIGH SCHOOL 4321 Walnut Avenue Irvine, CA 92604 (949) 936-7000 ext. 7074 [email protected] We understand and accept these policies and procedures. ___________________________ Signature of Student ___________________________ ___________________________ Signatures of Parents THE DO’S & DON’TS OF SCIENCE HOMEWORK There are two main reasons for doing homework: 1) to reinforce ideas introduced in class 2) to learn additional information or details that are not covered in class. There is no partial credit on homework - either it’s correctly done, or it’s not. To get credit for homework, it must be completed on time. “On time” means that it is ready to be examined on the next school day at the beginning of the period. “Completed” means that every answer must convey a self-explanatory idea. For example, these are not acceptable homework answers: He died in 1955. hydrogen a string of volcanic islands It has two moons. These are acceptable answers: Albert Einstein died in 1955. Hydrogen is the lightest element. Hawaii is a string of volcanic islands. Mars has two moons. If students have trouble formulating a sufficiently whole response, they may write the question first, then add their attenuated replies. The entire assignment must be written correctly for a student to receive any credit for it. I urge parents to read their child’s homework, not to check for scientific accuracy, but for clarity of thought, appropriate penmanship, and proper spelling. (Stew dents dew knot real eyes that Spellcheck dozen Noah they’re write ants her is.) Additionally, it’s my belief that learning should be shared. We acknowledge and understand this. STUDENT’S SIGNATURE PARENT’(S) SIGNATURE(S) MASS VS. WEIGHT MASS MEASURES HOW MUCH _____________ CONTAINS, BUT NOT HOW BIG IT IS. (“HOW BIG” = “_________”. THIS PILLOW IS BIG, BUT IT DOESN’T WEIGH MUCH.) IN THE METRIC SYSTEM (THE ONE SCIENTISTS AND MOST OF THE WORLD USES),_________________________________. WRITE THE MASS OF EACH OBJECT BELOW ITS PHOTO. “WEIGHT” IS A MEASURE OF _________________________________________. IT CAN BE WEAK (LIKE ON MARS) OR STRONG (LIKE ON JUPITER) OR ZERO (LIKE IN OUTER SPACE.) IT’S MEASURED IN __________ (IN THE ENGLISH SYSTEM) AND IN ______________ (IN THE METRIC SYSTEM). TYPICALLY A SPRING IS INVOLVED (EVEN IF YOU CAN’T SEE IT.) THAT’S WHY THE MEASURING DEVICE IS CALLED A _________________ . NOW WE KNOW WHAT MASS AND WEIGHT ARE, HOW THEY’RE MEASURED, AND IN WHAT UNITS. BUT HOW ARE THEY DIFFERENT? MASS VS. WEIGHT THE BOY’S BODY IS THE SAME ON THE EARTH AND MOON, SO HIS ____ REMAINS THE SAME. THE GRAVITY PULLING ON HIM DID CHANGE, THEREFORE HIS ________ CHANGED TOO. 2.2 LBS 1 KG 0.83 LBS 1 KG 0.37 LBS 1 KG 0 LBS 1 KG WE’RE NOT GOING TO WEIGH OURSELVES ON THE MOON, SO WHY SHOULD WE CARE ABOUT GRAVITY? NAME 2 MORE SPORTS AND HOW THEY’RE AFFECTED BY GRAVITY. READING A SCALE PROPERLY How important is precision? It depends what your motivation is. If you simply want to convey an idea, then saying “I paid around $300 for my snowboard.” is good enough. House prices are only accurate to the level of $10,000. (Look at house listings. Prices are in the form of $270,000. You don’t see them listed as $265,427.42 But gasoline prices are actually listed to the 1/10 cent. (e.g. $3.229/gallon). When reporting data, always give one level of precision more than the smallest unit indicated on the device. One level of precision more than a dollar would be a dime ($0.10). One level of precision more than a dime would be a cent ($0.01). For example, this graduated cylinder’s most precise line indicates 1 milliliter. So the volume read on here should be reported to the nearest 0.1 ml (like 65.3 ml). Each minor line on this water pressure gauge is 0.1 psi, so you can report its reading to the 0.01 psi (for example 10.47 psi). This clock has a line for every minute. So it’s more precise than this one These backyard thermometers may be pretty to look at, but they’re hard to read with precision. The temperatures go up by units of 10, so the best reading you’ll get is a unit of 1. What do you think the temperature reading on this flowery thermometer is? What’s the reading on this sunny one? The major lines on this grocery store produce scale indicate 1 kg. How much does each minor line represent? What is the level of precision that can be legitimately read on this scale? To what level of precision can this leaf be measured on this metric ruler? Accurately measure it and write the answer here: To what level of precision can this leaf be measured on this metric ruler? Accurately measure it and write the answer here: MENISCUS 3. ______________________ 3. ___________________________ Name: Date: Class: Laboratory Techniques Activity #10 Calculating the Surface Area and Volume of a Box The surface area is the part of the box that has the information is printed on it (e.g. the name of the cereal, nutritional information, etc.) The total surface area is the sum of all 6 sides. The volume measures how much material the box can hold. The sides of a box are rectangles, and the area of a rectangle is length x width. Assume the front of the box is 30cm tall and 22cm across. The side label (see the bar code at the bottom?) is also 30cm tall but only 8cm across. The surface area of the front panel is (30cm) x (22cm) = 660 cm cm (Remember the units undergo the same mathematical process that the numbers do.) But “cm cm” is written instead as “cm2” or “square cm”. Note that the back panel will have the same area as the front. What is the surface area of the left side? What is the surface area of the bottom of the box? What is the total surface area of the box? Volume is actually easier to calculate. Pick any corner on the box. I just randomly picked the corner indicated, but ANY corner is OK. Note that there are 3 edges touching it. Measure how long they are and then multiply them together. Volume = (30cm) x (22cm) x (8cm) = 5280 cm cm cm = 5280 cm3 = 5280 cubic cm. Continuing our breakfast theme, consider a stick of butter which is 11cm long with a square end meauring 4.5cm on each edge. What is its total surface area? What is its volume? MOTION Fast and getting faster or slower! Movement is all around us, from electrons to planets, so it’s an idea that scientists want to understand. Describe 3 more situations that illustrate something in motion: 1) 2) 3) How quickly something is moving is called its _________. (What kind of ticket do you get for driving too fast?) Make up an answer: How fast was the car going? You probably used “miles per hour” as the units. (It’s OK if you didn’t.) What does “miles” measure? What does “hour” measure? What does “per” mean? Making this more generalized, we can deduce that the equation for speed (or velocity) is: What could be some other units for speed? Do the sample math problems here: What if the speed of something keeps changing? The roller coaster car is going to ________________. ANY change in an object’s __________ counts as acceleration. Is this baseball player accelerating? Explain why. What about this one? Explain why. Three players walk off the field at the end of the game. Are they accelerating? Explain why. How can acceleration be calculated? It’s based on how much the speed changed and how quickly the change occurred. The formula is: If a car goes from 20 mph to 60 mph in 8 sec, what is its acceleration? Show your work here: Then the car cruises along at that speed (60 mph) for 10 sec. What is its acceleration? Seeing a red light ahead, the driver slows down from 60 mph to 45 mph in 5 sec. What is the car’s acceleration? A chart or a graph is a common way to depict an object’s motion. Luke Skywalker is riding in his landspeeder across the Tatooine desert. The data chart shows how far he was from his home at different times. Time (minutes) 10:00 10:05 10:08 10:11 10:25 10:30 Distance (Km) ) 0 10 15 23 47 62 This same information can be represented on a graph: Start with a 0 in the lower left corner. (Will it be zero for all graphs?) Label the vertical axis as “Dist. (Km)” and make each heavy line (not the minor lines) worth 10Km. Label the horizontal axis “Time (min)” and make each heavy line worth 2 minutes. What is the slant of the connecting graph line called? What is the equation to calculate the slope of a line? Draw a small “x” on the two spots of the slope that you’re going to use for the calculation. Don’t use data points as your 2 spots. Write the Y-values (the vertical numbers) here: Starting Y-value = Did Y get bigger or smaller? Ending Y-value = By how much? Do the same thing for the X-values for the two spots you chose. Starting X-value = Did X get bigger or smaller? Ending X-value = By how much? The slope of this graph is distance/time. What does that equal? Now calculate it. Remember to use the proper units. Thus, Luke’s landspeeder was going __________. Similarly, you can get the acceleration of an object if you have a graph with speed and time on it by calculating its slope. This graph depicts the motion of the roller coaster car on page 3 as it goes from point Y to point Z. Why doesn’t the slope line start at 0? How fast was the car moving at point Y? How would the graph of the car’s speed be different if the data showed its motion from point W to point X? Using the slope of the line, calculate the car’s acceleration. What did you get? Remember to use the proper units. CART & RAMP EXPERIMENT Galileo was very interested in studying gravity and the motion of free-falling objects. But gravity is fast and equipment during Galileo’s time (1564 – 1642) was slow (no stopwatches.) So he cleverly thought of using ramps to study the effects of the earth’s gravitational field, but slowed down. Likewise, we will use ramps to aid in our study. Each lab group will be analyzing a different configuration of the experiment. The ramp will be propped up on one end. Note that the wooden blocks are even with the edge of the track. Some groups will use 1 block, some will use 2, but all will be aligned as shown. QUESTION #1: Why is it important for all groups to follow this alignment rule? The purpose of this experiment is to determine what effect the angle of the ramp and the weight of the car have on the car’s acceleration down the ramp. To alter the weight, 1 or 2 bars of steel will be placed in the cargo area of the cart like this: Recall that to calculate acceleration, you need two speeds and the time it took to get from one speed to the other. You’ll use a stopwatch to time how long it takes to go from the top to the bottom of the ramp. Since the cart is being released, its initial speed is zero. How will the final speed be determined? The steel bars serve an additional function. They break the beam of light in an electronic timing gate. This beam was broken for 0.264 seconds. Using the yellow ruler affixed to the track, measure the length of the steel bar. Convert it from cm to m and then write that number here: Be sure that the beam is being broken by the steel bar (whose length you know) and not by the whole cart (whose length you don’t know). You can tell when the beam is being blocked because a red light on top of the timing gate will go on (see arrow). Here’s a close-up of the interior of the timing gate. (You can see the red light on top). The small hole at the bottom is where the beam of light comes out. The arrow is pointing to it. You can’t see the beam because it’s infra-red (just light the signal that goes from your remote to the TV.) That’s why you need to use the red indicator light to verify the correct alignment of the bar with the timing gate. Be sure that the steel bar isn’t still blocking the beam after the car hits the bumper at the end of the track. After everything’s set up, take the cart to the top of the ramp so its back end is also aligned with the edge of the track. Push the red “Reset” button on the timing gate. QUESTION #2: Why is it important that all groups release their carts from the same point? Release the cart and use the stopwatch to time how long it takes the cart to reach the bottom of the track. Record that number here: Since speed = distance / time, you can calculate the speed of the car upon impact because you have the distance (the length of the steel bar) and the time (from the electronic display on the timing gate.) Now use that final speed and the initial speed (which is 0) and the duration time (from the stopwatch) to calculate the cart’s acceleration. Do three runs and use the average data for your calculations. Write that number in the correct box on this chart and up on the whiteboard so other groups can copy your number (and copy theirs on your chart below). Circle the acceleration from your lab group (on this page, not the whiteboard). CART ACCELERATION (m/sec2) light cart (1 steel bar) heavy cart (2 steel bars) low angle high angle Conclusions and analysis: How did changing the angle of the ramp affect the cart’s acceleration? Explain this conclusion. How did changing the weight of the cart affect the cart’s acceleration? Explain this conclusion. Date & period the experiment was conducted: Names of all the people in your group: NEWTON’S LAWS Sometimes you want to know how fast an object is moving (called its “_____ ___”) Sometimes you care how fast AND what direction it’s moving in (called “___ ____”). Although “speed” and “velocity” are often used interchangeably, they’re not exactly the same thing because velocity includes _______ and speed doesn’t. For example, “30 mph heading west” is a _______. “30 mph” is a ______. Data that include a direction (like “force”) are called ________ quantities. Those that don’t (like “volume”) are called ________ quantities. Additional scalar quantities: Additional vector quantities: Like speed & velocity, mass & weight are also similar but not identical. Mass is a measure of how much ___ ___ makes up a material. Weight measures how strongly a ___________ field pulls on that material. An object will always have _ ___ _, but it might not have any ________. Where would an object have to be if it were weightless? Of mass and weight, which is a scalar and which is a vector? Gravitational fields cause mass (i.e. objects) to have weight. No gravity = no weight. Since gravity is all around us, we’d better know about it. Different planets have different gravity field strengths. Earth’s causes objects to accelerate at about 10 m/sec/sec. On the moon, it’s about 1.64 m/sec/sec. Mars is 3.73 m/sec2 and Jupiter’s gravity is 26 m/sec2! But on that planet (or moon) it’s the same for ALL objects. To quote Yoda, “Size matters ____”. If air friction is not significant, all objects will fall at the same rate. The reason why this is true will be explained later. But crazy Mr. Sacks will prove it now! Calculations with gravity (but first, a quick math review): Write the equation for calculating the speed of an object: Write the equation for calculating the acceleration of an object: Recall the archer on the first page. If he realeases the string and the arrow reaches a speed of 54 m/sec in 0.09 seconds, what was its acceleration? It continues at that speed (54 m/sec) flying across a field toward its target, which gets hit 2 seconds later. How far away was the target? The target stops the arrow in 0.60 seconds. What was the resultant acceleration of the arrow? By definition, a free-fall is one in which air friction is so small that it can be ignored (typically because the object is falling for a short distance, or because of its size or shape.) A boulder will readily freefall. A snowflake? Not even close! If an Olympian on a 3m high dive hits the water after free-falling for ¾ second, how fast will he be going when he makes a splash? Note that an object will lose speed on the way up just as quickly as it is gained on the way down. That’s why the path of a fly ball hit into the outfield or a pendulum is symmetrical. If a ball of pyrotechnic material is fired upward (like at a fireworks display), it will lose speed at the rate of -10 m/sec for every second it ascends, until it finally stops at its peak (called the “apex”). If a ball is shot up at 70 m/sec, how fast will it be going after 1 sec? How fast after 2 sec? After 5 sec? How long will it take to reach its apex? Now we can learn about a scientist who taught us a lot about movement: Galileo Galilei (1564 – 1642). Coincidently, he was born the same year as the famous British playwright shown here. Who is he? Galileo introduced the idea of “inertia”, from a word meaning “non-changing”. The non-changing aspect of matter is its motion. The more mass an object has, the harder it is to change its motion. Compare an empty shopping cart to one heavily loaded up like this one. Which would be harder to start moving? Which one (heavy or light) would be easier to keep going once it’s already moving? Which would be harder to turn? More mass means more inertia – more resistance to change in motion. That means ANY change in motion – speeding up or slowing down or turning. What’s a scientific synonym for “motion”? What previously-introduced term means the same as “a change in motion”? Hunters often use heavier bullets because they tend to keep on going, fighting against air friction, better than lighter bullets can. What’s the advantage of using a light tennis racket? What’s the disadvantage? NEWTON’S FIRST LAW: AN EXTERIOR FORCE APPLIED TO AN OBJECT WILL CHANGE THAT OBJECT’S MOTION. (IF MULTIPLE FORCES ARE BEING APPLIED, THEN THE RESULTANT FORCE WILL CHANGE THE MOTION.) NEWTON’S SECOND LAW: THE FIRST LAW SAYS: IF YOU PUSH ON AN OBJECT, ITS MOTION WILL CHANGE. THE SECOND LAW CALCULATES HOW MUCH IT WILL CHANGE. THAT AMOUNT DEPENDS ON HOW HARD YOU FORCE AND HOW HARD THE OBJECT CAN RESIST THE CHANGE. WHAT PHYSICS TERM IS SYNONYMOUS WITH “MOTION”? WHAT IS A SYNONYM FOR “CHANGE IN VELOCITY”? WHAT PROPERTY OF MATTER MAKES IT RESISTANT TO ACCELERATION? WHICH BALL HAS MORE INERTIA? WHY? INERTIA IS AN IMPORTANT FACTOR, BUT IT CAN’T BE MEASURED. WHAT IS IT RELATED TO THAT CAN BE MEASURED? ALL THESE IDEAS COME TOGETHER IN NEWTON’S 2ND LAW: F=ma NOTE THAT F & a ARE IN BOLD FONT, INDICATING THEY’RE VECTOR QUANTITIES AND m IS IN STANDARD FONT BECAUSE IT’S A SCALAR QUANTITY. WHAT’S THE DIFFERENCE BETWEEN A SCALAR AND A VECTOR QUANTITY? UNITS FOR THE EQUATION: ENGLISH: F=m a METRIC: IT TAKES 20N OF FORCE TO ACCELERATE A 10kg BOWLING BALL BY 2 m/sec2. HOW MUCH FORCE WOULD IT TAKE TO ACCELERATE A 500g BASEBALL BY 30 m/sec2? “WEIGHT” IS A COMMONLY ENCOUNTERED FORCE, CAUSED BY GRAVITATIONAL FIELDS. SO YOU CAN CALCULATE A WEIGHT USING A SPECIFIC FORM OF NEWTON’S SECOND LAW: w=m g “g” IS THE SAME 10 m/sec2 THAT WE STUDIED BEFORE. THUS, A 5KG BIKE WEIGHS 50N ON EARTH. ON JUPITER, g = 26 m/sec2, SO THE SAME BIKE WOULD WEIGH 130N. ONE POUND WEIGHS ABOUT 4 NEWTONS (ON EARTH). SO A QUARTER-POUNDER IS ALSO A NEWTON-BURGER! The exploding gunpowder in a cannon applies 6000N of force to the 4kg cannonball inside it. What will be the ball’s resultant acceleration? A woman throws a Frisbee for her dog to catch. If she exerts 5N of force on the 200g disc, how much will it accelerate? A dummy hangs from a tree, part of a Halloween display. If the dummy’s mass is 30kg, how much does it weigh? How much tension is in the rope? Is the dummy in static equilibrium or dynamic equilibrium? How do you know? A 400g football is thrown to a teammate at 6 m/sec. He catches the ball, stopping it in 0.2 seconds. How much force did he exert on it? Why is the force negative? Lois Lane has fallen from the roof of The Daily Planet. Superman flies down to save her before she splats onto the sidewalk below. Her mass is 50kg. If the net force on her is 150N upward, what will be her resultant acceleration? If she was moving 12 m/sec when he caught her, how many seconds will it take him to slow her down and stop her? Going from “Y” to “Z”, a roller coaster car has a resultant force of 2000N acting on it (pulling it down the hill). The mass of the car and the passengers totals 1000kg. If the car is going 7 m/sec at point Y, how fast will it be going when it reaches the bottom of the hill three seconds later? Medieval physics! A catapult team loads a 100kg rock into their weapon. To reach the enemy’s castle, the rock must be going 30 m/sec when it’s launched. But it’s in the bucket for only 1½ seconds before it flies out. How much force will the catapult need to supply to accomplish this? Bart uses his slingshot to launch a 70g rock with a force of 20N. If the launch takes 1/5 second, how fast will the rock be sailing through the air? Friction is a commonly-encountered factor in your life. Sometimes you want to maximize it and sometimes you want to minimize it. Sometimes you want both. List 2 more examples of helpful friction: 1) 2) List 2 more examples of unhelpful friction: 1) 2) Friction alters an object’s motion (whether you want it to or not!) In Physics, “motion” means _________. “altering an object’s velocity” means the same as ____________. According to Newton’s Second Law, what accelerates an object? Therefore, FRICTION IS A TYPE OF FORCE! Just like apples, bananas, and grapes are all classified as “fruits”, so are friction tension weight and buoyancy all examples of forces (there are others.) Since friction is a force, what would its units be? The amount of frictional force between two objects depends on: a) what the materials are (e.g. metal skates on the ice) b) how hard they’re pushed against each other. When you play duck-duckgoose, how is friction a necessary part of the game? Friction between the tires and the road give this car 1000 N of propellant force. If the car’s mass is 800kg, what will be its acceleration? How long will it take the car to reach 25 m/sec? A runner slides into 3rd base, incurring 75 N of frictional force. His mass is 50kg. What will his acceleration be? If he hit the ground going 3 m/sec, how long will it take him to stop? Can friction co-exist with other forces? Yes! Newton’s Third Law Newton’s First Law states that an object will maintain its velocity (whether it’s moving or not!) if there’s no net force acting on it. Newton’s Second Law says that if you decide that you DO want to change an object’s motion, the net force you’ll need to apply to that object depends on how hard it can fight against the force you’re applying (derived from its mass) and how quickly you want to change its motion (acceleration). In equation form, F = ma Newton’s Third Law says that the object will push back on you just as hard as you push on it. Kick a soccer ball. Sounds like fun! Kick a bowling ball. Ouch! Why? Kick a football. Go Irvine! Shooting a BB gun or a dart gun - not much kick. Firing artillery – A LOT OF KICK! But guns, even big guns, fired in the movies never kick. Why? (This is Indy shooting the swordsman in “Raiders of the Lost Ark”) Don’t forget about the Second Law! The cue ball (white) exerts a force on the 8-ball (black). So the black ball will accelerate. The black ball exerts the same amount of force back on the white, so the white ball’s motion changes too. How does this photo of 2 rams butting heads against each other illustrate each of Newton’s Laws? I) II) III) Figuring it out: The target shooter fires a 2kg gun which will launch 50g of lead at the flying clay disc. If the bullet accelerates out at 1000 m/sec2, what will be the resultant kick (acceleration) of the gun? Look sharp maties! Thar be pirates about! Cannons on ships are anchored to the walls by ropes. Why is that necessary? Note that the rope is loose before the cannon is fired (left photo) and tight after it’s been fired (right illustration). How did the rope get tight? Why not keep it tight from the beginning? Why must it start off loose? A 400kg cannon will fire a 5kg cannonball. But if the cannon kicks back faster than 8 m/sec2, its ropes will break the anchor bolts. What’s the greatest acceleration that the cannonball can have without exceeding the safety limit on the ropes? Give this problem a shot! (Hyarrr – Captain Sacks made a humorous quip, he did!) An octopus doesn’t have fins like fish do. How can it swim through the water? One last cannon conundrum: The acceleration of this 600kg cannon must be limited to 30 m/sec2 (or it will get too off-target for the second shot.) The amount of gunpowder loaded into it will ensure that requirement is met. The explosion lasts 0.02 seconds. How fast will an 8kg cannon ball fly out? A boy hits a piñata with 40N of force, causing the piñata to swing away. If the piñata’s mass is 5kg, how quickly will it accelerate away? If the boy’s broomstick has a mass of 2kg, what will its acceleration be upon impact? The player with the ball (#35) knocks his opponent (#12) off his feet. The airborne #12 has a mass of 100kg. He was running 6 m/sec but #35’s hit stopped him in 0.4 seconds. How much force did #35 exert against #12? How much force did #12 exert back on #35? What effect does #12’s force against #35 have against the latter? If #35 has a mass of 125kg and was running 5 m/sec before the impact, how fast was he running after the hit? In this illustration, which player is getting hit harder? INTRODUCTION TO WAVES Waves are all around us, even some you can’t see or feel. Give 2 examples of waves you can detect, and 2 you can’t. 1) 1) 2) 2) What is a wave? Waves transmit energy, not matter. Waves can be categorized in several ways: 1) How they’re grouped Specular Diffuse 2) How they travel Some waves must move through a material (like earthquakes). Some can pass across a vacuum (like light). 3) How they’re generated Forward & backward (called longitudinal) or side-to-side (called transverse). The material (if any) that a waves passes through is called its transmission medium. For an earthquake, it’s the ground. For music, it’s the air. Some waves, like light and heat, can travel through the emptiness of outer space. They’re called energy waves. Those that must travel through a substance, like sound or oceanic, are called matter waves. Most energy waves are transverse and most matter waves are longitudinal. When a crowd “does the wave”, is it a longitudinal or transverse wave? Matter or Energy wave? Note that the wave travels for 100’s of meters, but the people don’t. The energy is being transmitted, not the matter. Everything has parts. You learned that as a kid. (“Where’s your nose?” “Where’s your tummy?”) Waves have parts too. Crest – the highest measured value of the wave (e.g. highest voltage, brightest light, greatest pressure, etc.) Trough – shaped like the feed box, it’s the opposite of the crest. Wavelength – how long the wave is! (measured between 2 comparable points, like from one trough to the next). Symbol is (Greek lambda) Frequency – how frequently the wave is produced (2 times per second, 5 times per week, etc.) Symbol is f. Amplitude – the maximum distance from equilibrium. Symbol is A. “waves/sec” is such a common unit for frequency, that it has a shortened, eponymous unit called “Hertz” (abbreviated Hz). So 47 Hz = 47 waves/sec. The AM radio band is kHz and FM is MHz (“M” means “mega” which = million). The frequency of the radio wave that broadcasts 102.7 KIIS-FM is 102,700,000 Hz! speed = frequency x wavelength Waves travel at different speeds (the speed of light is about a million times faster than the speed of sound!) The speed is determined by the transmission medium. For example, a particular slinky will produce a specific speed. Shaking the slinky faster makes the frequency greater, but the wavelengths will also get smaller, so the two effects cancel out and you’re still left with the same final speed. Momma duck has a long stride (compared to the babies) but she moves her legs infrequently. The chicks have a short wavelength (the distance from one footprint to the next is small), but they move their legs frequently. This way all the birds have the same speed! MAJOR GROUPS OF WAVES The colors of light that we can see are a small part of a larger set of waves called the electromagnetic spectrum. All the waves in it are transverse energy waves. All sound and shock waves are longitudinal matter waves. Oceanic waves are a hybrid of transverse + longitudinal. There are 6 types of earthquake waves. Some types are transverse, some are longitudinal, and some are hybrids. And some you won’t learn about until college! DOPPLER SHIFT DISCOVERED BY CHRISTIAN JOHANN DOPPLER, IT EXPLAINS THE DIFFERENCE BETWEEN THE TRUE AND PERCEIVED FREQUENCY WHEN AN OBJECT AND OBSERVER ARE MOVING RELATIVE TO EACH OTHER. ANY WAVE CAN BE SHIFTED, BUT THE SPEED OF THE MOVER MUST BE SIGNIFICANT COMPARED TO THE SPEED OF THE WAVE; SO SOUND WAVES ARE MORE COMMONLY SHIFTED THAN LIGHT WAVES. When an earthquake occurs, the moving crustal plates can change the frequencies of the waves coming from the origin of the disturbance. Waves interact with their environment. Every time a wave enters a new material (i.e. transmission medium), some of its energy will bounce off and some will continue on. The part that bounces off the boundary surface is called the reflected wave. It turns out that the incoming wave (called the incident wave) enters at the same angle that the reflected wave bounces off. Anyone who’s played air hockey or pool has noticed this. When a wave enters a new transmission medium, its speed changes, which causes it to bend. This bending is called refraction. It’s how things like magnifying glasses work. This dual property of reflection and transmission is especially noticeable in glass. This phenomenon is called “Pepper’s Ghost” after Sir Henry Pepper (1821-1900). He used it to make the first believable ghost illusion on stage (“Hamlet” shown above and “A Christmas Carol” (in 1862!) below.) The Haunted Mansion also uses the effect. You’re on one side of the glass and the “hitchhiking ghosts” are on the other. The lights on your side illuminate you, then bounce off and go to the glass, then reflect again to your eye so you see yourself in the glass. Light on the ghosts’ side bounces off them and transmits through the glass to you! The grand ballroom is the largest “Pepper’s Ghost” in North America! The changing paintings in hallway are a transmission illusion. Two projectors shine onto the back of a blank canvas. You see only the transmitted light. One projector shows the normal image and the other shows the haunted image. As they take turns shining, the “painting” appears to be changing. Madame Leota in the séance room, and the singing busts in the graveyard are clever exploitations of reflection. They’re basically 3-D movies screens. When a movie of someone singing is projected onto it, the blank white head appears to be actually singing. Waves can also interfere with each other. An incoming wave approaching a beach will interfere with the retreating wave that preceded it. All the radio waves from different stations (KIIS-FM, POWER 106, etc.) are interfering with each other right now. The light waves of the different colors coming from your clothes are interfering. If the two interfering waves have different amplitudes from each other, you will get partial (instead of complete) constructive or destructive interference. But the effect is the same. For example, in (b) above, if the upper wave has an amplitude of +7 volts and the lower has an amplitude of -3 volts, then their resultant would be +4 volts. SOUND WAVES Sound waves are longitudinal / transverse matter / energy waves. Circle the correct answer. Circle the correct answer. They can reflect. Sonar and Radar are examples of this. What is a reflected wave called? (Hint: the answer is both a noun and a verb.) Geologists use reflection to determine how thick a layer of rock is. An explosive charge is detonated, and the time it takes to return (where it’s picked up by microphones) and the known speed of the shock wave are combined to figure out how far down the rock boundary is. If the speed of the wave is 4000 m/sec and the time between the blast and the echo is 25 milliseconds, how deep is the rock layer? A hungry dolphin is swimming after its breakfast. The speed of sound in water is 1500 m/sec. The dolphin stops and sends out a burst of waves which return in 0.1 seconds. How far away is the fish? 3 seconds later, it sends out another pulse which returns in 0.4 sec. How far away is the fish then? What is the speed of the fish? Is it moving toward or away from the dolphin? How do you know? Look at the green handout that lists the speed of sound in different materials. What three basic categories have the substances been broken into? What general conclusions can you make between the speed of sound through a material and what state of matter that material is? The speed of sound in air get faster as the air gets hotter. Why? The speed of sound in the positive temperature range can be calculated by this equation: speed = 331.5 m/sec + (0.6 m/sec/oC) (temperature of the air) Write your practice problems below: As we learned before, when a wave hits a new material, some of that wave will bounce back. And that returning wave can interfere with a subsequent incoming wave. This results in constructive and destructive interference (either partially or completely). Points of complete destructive interference are called nodes (like NO motion.) Points of completely constructive interference are called antinodes. When you’re jumping rope, your body is inside an antinode! What would your hands represent? When this type of wave interference pattern occurs, you don’t see a single pulse going from end to end anymore (those are called traveling waves). And instead what you get are wave patterns that just look like they’re flopping up and down (like the jump rope). So they’re called standing waves. Musical notes are all standing waves (produced by strings, air in a pipe, a drum head, etc.) The frequency that something naturally vibrates at is called its natural or fundamental frequency. When a string is plucked in the middle, it will vibrate at its natural frequency, also known as the First Harmonic (shown here as N= 1). It is the lowest frequency that can sustain a standing wave. That string can also vibrate at twice its fundamental frequency, called the Second Harmonic (N = 2). If the First Harmonic is 70 Hz, what is the frequency of the Second Harmonic? What is the frequency of the 4th Harmonic (N = 4)? Sound waves also refract. How much they bend, and in what direction, help us identify the different layers of the earth’s crust and interior. You can’t see around a doorway, but you can hear sounds around it. What wave phenomenon does this illustrate? When the cameraman yells “Action!”, the actor inside can hear him, but not see him. Why? The Inverse Square Law As a wave travels farther from its source, it seems to get weaker. Actually, total energy remains constant, but it gets spread out over an increasingly larger area. So its energy per square foot is reduced. As you get 4 times farther away, the energy is 4 squared or 42 = 4 x 4 = 16 times weaker. Five times farther away would show the energy per square foot is 25 times weaker. What would the energy be at 7 times the original distance? Sonic boom! Alexander Graham Bell (1847 – 1922) The unit for loudness is the Bel (named for Alexander Graham Bell), but we actually use only the decibel. These are decibel intensity levels of several sounds. Remember that both the loudness AND duration of a sound affect hearing loss. RESONANCE: CAUSING AN OBJECT TO VIBRATE AT ITS NATURAL FREQUENCY (OR A WHOLE-NUMBER MULTIPLE OF THAT FREQUENCY) BY SUBJECTING IT TO WAVES OF THAT FREQUENCY. THE INDUCED WAVE IS CALLED A SYMPATHETIC VIBRATION. LIGHT NOTES INTRODUCTION TO COLOR ALL CULTURES AND ALL RELIGIONS HAVE SOME EXPLANATION OF WHERE THE UNIVERSE STARTED. AND IT ALMOST ALWAYS INVOLVES LIGHT. SUN GODS ARE PROMINENT IN ALL POLYTHEISTIC RELIGIONS. (WHO IS THE EGYPTIAN SUN GOD SHOWN HERE?) EVEN THE ATHEISTIC SCIENTIFIC EXPLANATION INVOLVES LIGHT. WHAT’S THIS THEORY CALLED? WHY ARE BANANAS YELLOW AND CHERRIES RED AND BLUEBERRIES BLUE BUT ZEBRAS AND PANDAS AND POLAR BEARS AREN’T COLORED AT ALL? WHAT GIVES GOLD, SILVER, AND COPPER COLORS SO DISTINCTIVE THAT THEY’RE NAMED FOR THE METALS THEMSELVES? WHETHER IT’S COLORED OR NOT, EVERYTHING IS MADE OF ATOMS. AN ATOM OF GOLD IS DISTINCT AND DIFFERENT FROM AN ATOM OF ALUMINUM. HOW? A PARTICLE OF LIGHT IS CALLED A PHOTON (LIKE THE PHOTON TORPEDOES ON “STAR TREK”.) WHAT ART FORM GETS ITS NAME FROM THIS DEFINITION? A COLOR IS JUST A PARTICULAR FREQUENCY OF ENERGY THAT A PART OF OUR BODY CAN PERCEIVE (LIKE SOUND WAVES). THE ATOMS IN A CHERRY HAVE A UNIQUE CONFIGURATION THAT ALLOWS ONLY SMALL ELECTRON JUMPS, THEREBY RESULTING IN A SMALL ENERGY COLOR (RED). LIKEWISE, A BLUEBERRY DOESN’T TASTE LIKE A CHERRY BECAUSE IT’S MADE OF DIFFERENT SET OF ATOMS AND MOLECULES. ITS CONFIGURATION WILL NOT ALLOW SMALL JUMPS, ONLY BIG. THIS RESULTS IN THEIR HIGH ENERGY COLOR (BLUE). WHAT SIZE JUMP DO YOU THINK HAPPENS IN GREEN GRAPES? WHY? LASER PRODUCES A VERY SPECIFIC FREQUENCY (AND THEREFORE COLOR). IT’S LIKE A TUNING FORK, BUT FOR COLOR. THIS IS WHY THEY CAN BE USED TO REMOVE TATTOOS. JUST AS SINGING THE RIGHT PITCH CAN BREAK A WINE GLASS, OPTICAL RESONANCE CAN DESTROY THE PIGMENTED CELLS IN A TATTOO. IF YOU MIX ALL THE COLORS OF LIGHT TOGETHER, YOU GET WHITE LIGHT. WHY ISN’T THIS TRUE FOR PAINT? YOU CAN ALSO “RUN IT BACKWARDS” AND SPLIT UP WHITE LIGHT AND SEE ITS COMPONENT COLORS. THIS PROVES THAT WHITE LIGHT IS THE COMBINATION OF ALL THE COLORS – IT CONTAINS ALL THE COLORS OF LIGHT. THE SUN’S WHITE LIGHT PRODUCES ALL THE COLORS OF THE RAINBOW. THE LEAVES ON THE BLUE-BERRY BUSH ABSORB ALL THE WHITE’S COLORS, BUT RE-EMIT ONLY THE GREEN COMPONENT. WHY? SIR ISAAC NEWTON USING A PRISM TO STUDY THE BEHAVIOR OF LIGHT. TWO LIMOSINES ARE PARKED OUTSIDE A WEDDING RECEPTION. SITTING UNDER THE SAME SUN, WHICH ONE WILL GET HOTTER? WHY? LASER + BLACK + WHITE = BAR CODE! SAMUEL MORSE (1791 – 1872) RECALL THE RESONANCE EXPERIMENT. IT SHOWED THAT THE SPEED OF A WAVE DEPENDS ON THE MEDIUM, NOT THE WAVE. ELECTROMAGNETIC WAVES (WHICH INCLUDE LIGHT) TRAVEL FASTEST THROUGH A VACUUM. WHY? LIGHT WILL TRAVEL FASTER IN HOT AIR THAN IN COLD. WHY? ALSO RECALL THAT WHEN ANY WAVE ENTERS A NEW MEDIUM, IT WILL BEND (TOWARD THE NEW MATERIAL IF IT SLOWS DOWN, AND AWAY FROM THE NEW MEDIUM IF IT SPEEDS UP.) WHAT’S THE SCIENTIFIC WORD FOR THE BENDING OF A WAVE AS IT ENTERS A DIFFERENT MEDIUM? WHEN AIR (OR ANY FLUID) IS HEATED, IT WILL RISE – BUT NOT IN A STRAIGHT LINE. SO SOME AREAS WILL BE WARMER THAN OTHERS. SO LIGHT WILL MOVE FASTER IN SOME PLACES THAN OTHERS. AND IT WILL BEND WHEN IT HITS AN AREA OF A DIFFERENT TEMPERATURE. THAT’S WHAT CAUSES THE DISTORTION YOU SEE WHEN THE AIR IS HOT. THIS IS ALSO WHAT CAUSES MIRAGES. IT TURNS OUT THAT MORE FREQUENCY MEANS MORE BENDING, SO HIGHER FREQUENCIES REFRACT MORE THAN LOWER ONES DO. THIS PHENOMENON IS CALLED “DISPERSION”. WHICH COLOR BENDS THE MOST WHEN IT’S REFRACTED? RAINBOWS ARE THE RESULT OF DISPERSION AND REFLECTION. (NOTE THAT RED IS ALWAYS BENT THE LEAST AND VIOLET THE MOST.) REFRACTION, SCATTERING, AND DISPERSION ALSO EXPLAIN WHY THE SKY IS BLUE AND SUNSETS ARE RED. (DO YOUR HOMEWORK TONIGHT AND YOU’LL FIND OUT HOW!) ANOTHER USEFUL EXPLOITATION OF REFRACTION INVOLVES LENSES. WE’LL STUDY TWO BASIC SHAPES OF LENSES: CONVERGING (CONVEX) (Who is this famous fictional detective?) AND DIVERGING (CONCAVE). THINK OF A LENS CENTERED ON A COORDINATE AXIS. THE X-AXIS IS ALSO CALLED THE PRINCIPLE AXIS. RAYS OF LIGHT THAT COME IN PARALLEL TO THE X-AXIS WILL PASS THROUGH A CONVERGING LENS AND ALL HEAD TOWARD A SINGLE POINT CALLED THE FOCAL POINT. THE FOCAL LENGTH OF A LENS IS THE DISTANCE FROM THE ORIGIN TO THAT FOCAL POINT. IT IS LISTED AS A POSITIVE NUMBER (FOR EXAMPLE +5cm OR +4 INCHES). FOR A DIVERGING LENS, THE PARALLEL RAYS WILL ALL POINT AWAY FROM A SINGLE SPOT. IT’S STILL CALLED A FOCAL POINT, BUT THE FOCAL LENGTH OF A DIVERGING LENS IS A NEGATIVE NUMBER (LIKE -6cm). THOSE RAYS DON’T REALLY EMANATE FROM THE FOCAL POINT, SO THEY’RE SAID TO PRODUCE A VIRTUAL IMAGE. RAYS COMING FROM A CONVERGING LENS REALLY DO PASS THROUGH THE FOCAL POINT, SO THEY FORM A REAL IMAGE. LENSES ALSO HAVE A RADIUS OF CURVATURE. IT’S EQUAL TO THE RADIUS OF THE CIRCLES WHOSE INTERSECTION HAVE THE SAME SHAPE AS THE LENS. TODAY YOU’LL LEARN HOW TO DRAW A PROPERLY-SIZED SYMMETRICAL LENS CENTERED ON ITS COORDINATE AXIS. LIKE CONVERGING LENSES, CONVERGING MIRRORS PRODUCE REAL IMAGES AND REFLECT PARALLEL RAYS TOWARD A SINGLE POINT. THEY ARE USED FOR SATELLITE DISHES AND THE BOWLS OF FLASHLIGHTS & SEARCHLIGHTS. JUST LIKE DIVERGING LENSES, DIVERGING MIRRORS SPREAD OUT THE PARALLEL LIGHT RAYS THAT HIT IT. THEY ARE USED FOR SECURITY & SAFETY, LIKE TO SEE AROUND CORNERS IN HALLWAYS & PARKING STRUCTURES, IN THE QUICKIE MART, AND THE SIDE-VIEW MIRRORS OF CARS. LIGHT WAVES LEAVE A SOURCE IN MULTIPLE ORIENTATIONS. A POLARIZING FILTER CAN ELIMINATE UNWANTED ONES. CERTAIN ORIENTATIONS OF LIGHT WAVES PRODUCE GLARE. POLARIZING GLASSES (OR FILTER) CAN ELIMINATE THEM SO YOU CAN SEE MORE CLEARLY. RECALL THE DIFFRACTION OF WAVES (THEY BEND AS THEY GO THROUGH A BREAK IN A BOUNDARY). THE AMOUNT OF DIFFRACTION IS DETERMINED BY HOW CLOSE THE WAVELENGTH IS TO THE LENGTH OF THE GAP. THE WAVELENGTH OF LIGHT IS VERY SMALL (COMPARED TO SOUND) FROM 400nm FOR VIOLET TO 650nm FOR RED. “nm” IS SHORT FOR “NANOMETER” = “MILLIONTH OF A METER” FOR COMPARISON, YOUR HAIR IS ABOUT 75nm THICK. SO A VERY SMALL GAP WILL DIFFRACT LIGHT. ADMITTEDLY, THIS PHENOMENON BY ITSELF MAY BE UNIMPRESSIVE, BUT COMBINED WITH DISPERSION, IT ALLOWS SCIENTISTS TO FIGURE OUT WHAT’S INSIDE DISTANT STARS, IDENTIFY UNKNOWN MATERIAL, DISTINGUISH FAMOUS ARTWORK FROM FRAUDS, ETC…. REMEMBER THAT DIFFERENT ELEMENTS WILL LOOK DIFFERENT (E.G. SILVER VS. GOLD) BECAUSE OF THEIR ATOMIC CONFIGURATION (PRIMARILY HOW MANY ELECTRONS IT HAS AND WHERE THEY JUMP AND FALL WHEN IT’S ILLUMINATED). LIKE A CHORD IN MUSIC, AN ILLUMINATED ELEMENT MAY PRODUCE SEVERAL FREQUENCIES OF LIGHT. A DIFFRACTION GRATING CAN SPLIT THEM UP, REVELING THE INDIVIDUAL COLORS UNIQUE TO THAT ELEMENT. A VERTICAL BEAM OF WHITE LIGHT SHINING ON A SCREEN A VERTICAL BEAM OF WHITE LIGHT PASSING THROUGH A DIFFRACTION GRATING, THEN SHINING ON A SCREEN. A VERTICAL BEAM OF LIGHT FROM A COLORED SOURCE (E.G. A NEON SIGN) PASSING THROUGH A DIFFRACTION GRATING, THEN SHINING ON A SCREEN. A SPECTROSCOPE USES A DIFFRACTION GRATING TO SPLIT UP LIGHT COMING FROM A SOURCE SO ITS UNIQUE COMBI-NATION OF COLORS CAN BE BROKEN DOWN AND COMPARED TO KNOWN STANDARDS FOR IDENTIFICATION. IT’S LIKE IDENTIFYING THE INGREDIENTS IN BBQ SAUCE. LOOK AT HYDROGEN’S SPECTRUM. IF YOU HAVE A MYSTERY LIGHT WHICH CONTAINS THOSE 4 LINES IN THOSE SAME PLACES, THEN IT CONTAINS HYDROGEN (AND POSSIBLY OTHER STUFF). DETECTIVES WHO FIND A WEAPON WITH DIFFERENT FINGERPRINTS ON IT HAVE TO FIGURE OUT WHO HELD IT – THIS IS THE SAME IDEA. THIS IS NOT A NEW IDEA. SPECTROSCOPES HAVE BEEN AROUND FOR A LONG TIME. SOME ARE FANCY AND SOME ARE COMPLEX. BUT THEY ALL WORK OFF THE SAME PRINCIPLE. ELECTRICITY THIS POWER SOURCE IS COMMON (AND COMMONLY UNDERSTOOD) TODAY, BUT OUR KNOWLEDGE OF IT STARTED AROUND THE SAME TIME AS SOUND WAVES (LIKE CHRISTIAN DOPPLER) AND FORCES (LIKE ISAAC NEWTON) AND OTHER SCIENTIFIC DISCOVERIES. ONE OF THE MOST FAMOUS EXAMINERS OF ELECTRICITY IS THAT GUY ON THE $100 BILL. BEN FRANKLIN THOUGHT LIGHTNING AND ELECTRICITY WERE THE SAME THING (HE WAS RIGHT). HE ALSO THOUGHT THAT ELECTRICITY WAS MADE OF POSITIVE PARTICLES (LIKE PROTONS) – HE WAS WRONG ABOUT THAT ONE. ELECTRICITY IS ELECTRONS. ELECTRICITY IS MADE OF ELECTRONS MOVING THROUGH A WIRE. BUT REMEMBER THAT THE WIRE IS MADE OF ATOMS AND THEY CONTAIN ELECTRONS TOO. AND ALL ELECTRONS ARE CREATED EQUAL. SO WHEN ELECTRONS (ELECTRICITY) COMES OUT OF A BATTERY OR A LIGHT SOCKET OR A WALL OUTLET, THEY MOVE THROUGH A WIRE THAT ALREADY CONTAINS ELECTRONS. IT’S LIKE A PIPE FILLED WITH IDENTICAL MARBLES. EVERY NEW MARBLE THAT ENTERS THE PIPE WILL SHOVE ALL THE OTHER MARBLES (ELECTRONS) DOWN THE PIPE AND ONE WILL POP OUT THE OTHER END. HOW HARD THOSE ELECTRONS ARE FORCED INTO THE WIRE IS CALLED VOLTAGE AND HOW MANY ARE MOVING IS CALLED THE CURRENT. THE MARBLE THAT GETS PUSHED OUT IS BASICALLY A DEAD ELECTRON. IT STILL EXISTS, BUT IT HAS NO POWER LEFT. WHEN ALL THE ELECTRONS HAVE FLOWED FROM ONE END OF THE BATTERY TO THE OTHER, THE BATTERY IS DEAD. ELECTRONS DON’T TRANSFORM INTO LIGHT (OR HEAT OR MOTION, ETC.). THEIR ELECTRICAL ENERGY IS JUST CONVERTED INTO SOME OTHER KIND OF ENERGY (KINETIC, ACOUSTIC, THERMAL, ETC.) THE FALLING WATER SHOWN HERE DOES WORK ON THE PADDLE WHEEL SO IT CAN SPIN (AND THEN THE WHEEL CAN GRIND GRAIN OR MAKE THE BORES OF CANNON BARRELS, ETC.) THE WATER AT THE BOTTOM OF THE WHEEL STILL EXISTS, BUT ITS GRAVITATIONAL ENERGY HAS BEEN CONVERTED TO SOMETHING ELSE (THE WHEEL’S KINETIC ENERGY.) INTRODUCTION TO MAGNETISM AFTER GRAVITY, MAGNETISM IS ONE OF THE FIRST FORCES THAT YOU BECOME AWARE OF. LIKE ELECTRICAL FIELDS, MAGNETIC FIELDS CREATE FORCES ON CERTAIN OBJECTS THAT ENTER THEM. THE EARTH’S MAGNETIC FIELD IS NOT AS STRONG AS ITS GRAVITATIONAL FIELD, BUT IT EXTENDS FAR BEYOND THE PLANET’S SURFACE. WHAT MAKES A MAGNET? IN 1820, HANS CHRISTIAN OERSTED PERFORMED AN EXPERIMENT WHICH SHOWED THAT WHEN A CURRENT FLOWS THROUGH A WIRE, A MAGNETIC FIELD EMANATES FROM THE WIRE. RECALL THAT A CURRENT IS JUST ELECTRONS FLOWING. YET ALL ATOMS CONTAIN MOVING ELECTRONS (WHICH ARE BASICALLY JUST TINY ELECTRIC CIRCUITS), SO WHY ISN’T EVERYTHING MAGNETIC? BECAUSE MOST OF THE TIME, THE ATOMIC MAGNETIC FIELDS CREATED BY THE ELECTRONS ARE RANDOMLY ORIENTED, SO THEY CANCEL EACH OTHER OUT. IN A MAGNET, THE LITTLE ATOMIC MAGNET FIELDS ARE ORGANIZED, ALL POINTING IN THE SAME DIRECTION AND THUS WORKING TOGETHER. ALL ELEMENTS PARAMAGNETIC (ALIGN IN AN EXTERNAL MAGNETIC FIELD) Co, U+4, Fe, Ni, Al, O, Na, Cu+1, … FERROMAGNETIC (REMAIN ALIGNED AFTER THE MAGNETIC FIELD IS REMOVED) Fe, Ni, Co THE FAMOUS EXPERIMENT PERFORMED BY THAT GREAT DANE, HANS CHRISTIAN OERSTED (1777 – 1851) IN 1820 SHOWED THAT ELECTRICITY COULD MAKE MAGNETISM. THIS PHENOMENON IS EXPLOITED IN ELECTROMAGNETS, WHICH ARE PART OF CONSTRUCTION & DEMOLITION, TAPE DECK HEADS, MRI MACHINES, BULLET TRAINS, MICROWAVE OVENS, AND LOTS OF OTHER COOL THINGS. INDUCED VOLTAGE SO OERSTED PROVED THAT MOVING ELECTRONS (e.g. A CURRENT) CAN PRODUCE A MAGNETIC FIELD. IT TURNS OUT THAT THE REVERSE IS ALSO TRUE - A MOVING MAGNETIC FIELD CAN PRODUCE A CURRENT. THE FORMER PHENOMENON IS EXPLOITED IN A MOTOR. THE LATTER IS THE IDEA BEHIND A GENERATOR. THIS TYPE OF CURRENT PRODUCTION IS CALLED “ELECTROMAGNETIC INDUCTION”. Ford Model T 1908 - 1927 THE BIG PICTURE ELECTRIC FIELDS AND MAGNETIC FIELDS ARE THE INGREDIENTS IN ALL ELECTROMAGNETIC RADIATION. LIGHT WAVES, X-RAYS, RADIO WAVES, HEAT, ETC. ARE TORRENTS OF THESE TWO FIELDS TRAVELLING TOGETHER IN TRANSVERSE FASHION: HAVING LEARNED ALL ABOUT LENSES AND MIRRORS, WHAT CAN WE DO WITH THEM? WE CAN LOOK AT THINGS THAT ARE VERY SMALL & CLOSE AND LARGE & DISTANT. A TELESCOPE DOES THE LATTER. WHAT DOES THE FORMER? (I.E. LOOK AT THINGS VERY SMALL & CLOSE?) TELESCOPES HAVE BEEN AROUND SINCE THE 1500’S (POSSIBLY EARLIER), SO THEY’RE NOT VERY COMPLEX. BY THE 1600’S, THEY WERE IN COMMON USE BY PIRATES, SCIENTISTS, MARINERS AND ANYONE ELSE WHO WANTED TO SEE THINGS AT A DISTANCE. NOW THEY CAN BE AS SMALL AS TOILET PAPER TUBE OR AS BIG AS A BUS. ANOTHER NAUTICAL TOOL IS CALLED A SEXTANT. IT WAS INVENTED IN 1757 AND USES MIRRORS AND A LENS TO TAKE SIGHTINGS FROM THE SUN AND STARS IN ORDER TO FIND ONE'S LATITUDE AND LONGITUDE. SEXTANTS MEASURE THE ANGLE BETWEEN TWO OBJECTS. THESE MEASUREMENTS ALLOWED NAVIGATORS TO PLOT A COURSE ON A CHART. TO FIND LATITUDE, SIGHTINGS ARE MADE BETWEEN THE HORIZON AND A STAR OR THE SUN. LATITUDE IS FOUND BY TAKING A MEASUREMENT BETWEEN THE MOON AND A STAR. NO NEED FOR G.P.S.! THERE ARE 2 BASIC TYPES OF TELESCOPES THAT WE COVER IN THIS CLASS: REFRACTING AND REFLECTING (WHICH IS EXACTLY WHAT LENSES AND MIRRORS DO!) THE MAGNIFICATION OF A TELESCOPE IS THE FOCAL LENGTH OF THE OBJECTIVE LENS OR MIRROR (WHY IS IT CALLED THE “OBJECTIVE”?) DIVIDED BY THE FOCAL LENGTH OF THE EYEPIECE LENS Practice problems: A telescope has an objective focal length (OFL) = 250mm and an eyepiece focal length (EFL) = 100mm, what is its magnification? OFL = 75mm and EFL = 15mm. M = ? EFL = 8” and OFL = 32”. M=? THIS IS A REFLECTING TELESCOPE. RECALL THAT MIRRORS HAVE FOCAL POINTS TOO. THEY USE THE SAME MAGNIFICATION EQUATION. EXTEND THE RAYS GOING FROM THE CONVERGING MIRROR TO THE FLAT MIRROR AND INDICATE WHERE ITS FOCAL POINT IS. TIME FOR A VIDEO! PLANETS AND STARS ARE AFFECTED BY GRAVITY, BUT WHY SHOULD WE CARE? WE KNOW THAT WHEN WE WANT TO LAUNCH AN OBJECT OVER A DISTANCE, WE MUST GIVE IT SOME UPWARD VELOCITY TO GIVE IT TIME TO MOVE BEFORE GRAVITY BRINGS IT BACK DOWN AGAIN. NOTE THAT GRAVITY ONLY PULLS THESE OBJECTS DOWN. IT HAS NO HORIZONTAL INFLUENCE. THE VERTICAL AND HORIZONTAL COMPONENTS OF THE OBJECT’S MOTION ARE INDEPENDENT OF EACH OTHER. THE EARTH’S SURFACE CURVES AROUND. IT DROPS DOWN ABOUT _____ FOR EVERY _____ YOU MOVE LATERALLY. WHICH GREEK GOD IS SHOWN HERE HOLDING UP THE EARTH? FAMOUS GRAVITY GURU ISAAC NEWTON PONDERED THAT EVEN WITHOUT ANY VERTICAL COMPONENT, A CANNONBALL FIRED HORIZONTALLY WOULD STILL TRAVEL SOME DISTANCE BEFORE HITTING THE DIRT. WHAT WOULD HAPPEN IF THE CANNONBALL WERE FIRED SO FAST THAT ITS PARABOLIC PATH MATCHED THE CURVATURE OF THE EARTH? WHAT IF IT TOO TRAVELED 8Km AS IT DROPPED 5m? IT TURNS OUT THAT THIS MAGICAL SPEED IS 8 Km/sec (AROUND 18,000 MPH!) TOO FAST FOR BULLETS OR CANNONBALLS, BUT EASILY ACCOMPLISHED BY SATELLITES. SPEEDS FASTER THAN 8 Km/sec WILL RESULT IN AN OVAL ORBIT (CALLED AN ELLIPSE.) LIKEWISE, THE MOON IS “FALLING” AROUND THE EARTH, AND ALL THE PLANETS ARE “FALLING” AROUND THE SUN! THAT’S WHY WE CARE ABOUT GRAVITATIONAL FIELDS. THEY AFFECT THE MOTION OF DARN NEAR EVERYTHING IN THE WHOLE UNIVERSE! IT TURNS OUT THAT ALTHOUGH PLANETS AND MOONS ARE TYPICALLY ILLUSTRATED ORBITING IN CIRCULAR PATHS, THEY VERY RARELY ARE. THE ORBIT IS TYPICALLY AN ELLIPSE. AN ELLIPSE IS DIFFERENT FROM A CIRCLE BECAUSE IT HAS TWO “CENTERS”. THEY’RE ACTUALLY CALLED FOCI (PLURAL OF FOCUS.) RECALL THAT A CIRCLE IS MADE FROM ALL THE POINTS IN A PLANE THAT ARE EQUALLY DISTANT FROM A FIXED POINT. WHAT IS THAT FIXED POINT (THE CENTER DOT) CALLED? WHAT ARE THE LINES CALLED? AN ELLIPSE IS A STRETCHED-OUT CIRCLE, SO THE CENTER GETS STRETCHED OUT TOO. THE INTERIOR DOTS ARE THE FOCI. THE TOTAL DISTANCE FROM THE FOCI TO ANY POINT ON THE ELLIPSE IS A CONSTANT NUMBER. THAT NUMBER IS ALSO EQUAL TO ANOTHER IMPORTANT DISTANCE CALLED THE MAJOR AXIS. FILL IN THE MISSING ADJECTIVES IN THIS DIAGRAM: THE MAJOR AXIS IS TWICE AS LONG AS THE __________________. A COMPASS IS A GREAT TOOL FOR DRAWING A CIRCLE, BUT IT WON’T HELP YOU DRAW AN ELLIPSE. BUT TWO NAILS AND A PIECE OF STRING WILL HELP YOU MAKE A NIFTY OVAL! WHAT PART OF THE ELLIPSE DO THE NAILS REPRESENT? AND NOW, TIME FOR A FINAL QUICK VIDEO! RECALL NEWTON’S FIRST LAW: OBJECTS MAINTAIN THEIR MOTION FOREVER IF THERE’S NO OUTSIDE FORCE ACTING ON THEM. THE AIR HOCKEY PUCK CONTINUES IN A STRAIGHT LINE AT A CONSTANT SPEED UNTIL THE WALL OR A PADDLE HITS IT. GOING AROUND IN A CIRCLE IS A CONTINUAL CHANGE IN MOTION BECAUSE THE OBJECT’S DIRECTION IS CONSTANTLY CHANGING, AND THAT REQUIRES A CONTINUAL APPLICATION OF AN OUTSIDE FORCE. IN EACH PHOTO, DRAW AN ARROW REPRESENTING THAT FORCE. START THE ARROW IN THE MIDDLE OF THE OBJECT THAT’S CIRCLING AROUND, AND POINT IT ALONG THE LINE OF THE APPLIED FORCE (AS SHOWN IN THE PHOTO BELOW). NOTICE HOW THE FORCE ALWAYS POINTS TOWARD THE CENTER OF THE CIRCLE. “CENTER POINTING” MEANS “CENTRIPETAL” IN GREEK. FOR CELESTIAL BODIES, THAT CENTRIPETAL FORCE IS GRAVITY. WITHOUT THE GRAVITATIONAL PULL FROM THE SUN, ALL THE PLANETS WOULD FLY AWAY WITH A VELOCITY THAT’S TANGENT TO THE ORBIT THEY WERE MAKING WHEN THE GRAVITY GOT TURNED OFF. THE MOVEMENT OF PLANETS AROUND STARS (OR MOONS AROUND PLANETS) IS THE RESULT OF A TUG-OF-WAR BETWEEN NEWTON’S FIRST AND SECOND LAWS: THE TENDENCY OF AN OBJECT TO MAINTAIN ITS VELOCITY, AND HOW THAT VELOCITY IS CHANGED WHEN A FORCE ACTS ON IT. AMAZINGLY, GRAVITATION FIELDS CAN EVEN AFFECT THE MOTION OF LIGHT (WHICH DOESN’T HAVE ANY MASS!) NEWTON WOULDN’T HAVE BELIEVED IT, BUT EINSTEIN PREDICTED IT (AND HE WAS RIGHT). OUR NEXT VIDEO DISCUSSES HIS HYPOTHESIS AND THE EXPERIMENT THAT MADE ALBERT EINSTEIN FAMOUS (NOT JUST IN THE SCIENTIFIC COMMUNITY, BUT AROUND THE WORLD.) THE PHENOMENON IS CALLED “GRAVITATIONAL LENSING” BECAUSE EXTREMELY LARGE GRAVITATIONAL FIELDS CAN BEND LIGHT JUST AS A LENS DOES. COMPARED TO OTHER FORCES (LIKE MAGNETIC OR ATOMIC), GRAVITY IS A VERY WEAK FORCE (ALTHOUGH ITS REACH IS QUITE IMPRESSIVE.) WE WON’T BE CALCULATING IT IN THIS CLASS, BUT THE GRAVITATIONAL FORCE BETWEEN TWO OBJECTS DEPENDS ON THEIR MASSES AND HOW FAR APART THEY ARE. NOTE THAT THIS EQUATION HAS THE SAME DENOMINATOR AS THE EQUATIONS FOR THE SPREADING OF LIGHT AND SOUND WAVES (INVERSE SQUARE.) WHAT’S THE “G” FOR? CONSIDER THIS COMPARISON: BIGGER CIRCLES HAVE BIGGER DIAMETERS. A DIAMETER AND A CIRCUMFERENCE ARE NOT THE SAME LENGTH, BUT THEY ARE RELATED. HOW? BY THE EQUATION C = D THE EQUATION C = D IS WRONG. THE NUMBER MAKES IT RIGHT. THE “G” IN THE GRAVITY EQUATION SERVES THE SAME PURPOSE – IT’S A CONSTANT JUST LIKE IS, AND IT INTRODUCES THE CORRECT BALANCE TO MAKE THE EQUATION TRUE. HOW WEAK IS GRAVITY? G = 0.0000000000667! THAT’S WHY YOU NEED A LOT OF MASS TO EXHIBIT A READILY NOTICEABLE GRAVITATIONAL FIELD. ALTHOUGH PETER GRIFFIN SEEMS TO DOUBT THAT. BUT ALL OBJECTS HAVE MASS AND THEREFORE A GRAVITATION FIELD AROUND THEM. IN “STAR WARS”, YODA EXPLAINED TO LUKE THAT THE FORCE WAS EVERYWHERE – HE WAS RIGHT. WISE JEDI WAS HE. JUST AS MAGNETS WILL MOVE FASTER AS THEY GET CLOSER TOGETHER AND A FALLING BODY SPEEDS UP AS IT GETS CLOSER TO THE EARTH, AN ORBITING BODY WILL SPEED UP AS IT GETS CLOSER TO THE SUN. THE OTHER “CENTRAL” IDEA WE NEED TO INTRODUCE IS CALLED ANGULAR MOMENTUM. INDIANA JONES KNOWS ABOUT LINEAR MOMENTUM. RELATED TO NEWTON’S 2ND LAW, IT IMPLIES THAT SMALLER OBJECTS MOVE FASTER THAN LARGER ONES GIVEN THE SAME FORCE. SO AS THE WHIP GETS SMALLER, IT GOES FASTER. ICE SKATERS, GYMNASTS, HIGH-DIVERS, AND CATS UNDERSTAND ANGULAR MOMENTUM. AS THEIR RADIUS GETS SMALLER, THEY SPIN FASTER. A FALLING CAT WILL WITHDRAW AND STRETCH ITS LEGS AND TORSO TO SPIN ITSELF AT THE RIGHT SPEED AT THE RIGHT TIME SO IT LANDS ON ITS FEET. THE TAIL HELPS TOO. CATS THAT FALL OUT OF APARTMENTS ABOVE THE 2ND FLOOR ACTUALLY HAVE A HIGHER SURVIVAL RATE THAN THOSE WHO FALL SHORTER DISTANCES BECAUSE THEY HAVE MORE TIME TO GET THEIR FEET UNDER THEM BEFORE THEY LAND. JUST LIKE BUBBLES GOING DOWN A DRAIN, AS PLANETS (OR OTHER CELESTIAL BODIES) GET CLOSER TO THE SUN, THEY MOVE FASTER. AN INVERSE RELATIONSHIP EXISTS BETWEEN THE PLANET’S SPEED AND ITS DISTANCE FROM THE SUN. IF THE PLANET DOUBLES ITS DISTANCE, IT WILL GO HALF AS FAST. AT ¼ THE DISTANCE, IT WILL GO 4 TIMES FASTER. PLANETARY IDENTIFICATION LAB Purpose: Your job will be to identify each object on the following pages (Object A, Object B, and Object C) based upon their orbital characteristics. Procedure: ON THE DIAGRAM OF THE ORBIT FOR EACH OBJECT, DO THE FOLLOWING: 1. Using the colored pens provided, draw the “crosshairs” and label them as shown. Draw the Major Axis in black, the Minor Axis in blue, and the Semi-Major Axis in red. Do not draw the SemiMajor Axis (SMA) through the sun. 2. Measure the length of the SMA in centimeters and record it where indicated on the back of this page. Remember that this is the planet’s average distance away from the sun. 3. Measure the distance from the center of the ellipse to the sun (in centimeters) and record it likewise. 4. Divide the smaller number by the bigger one to calculate the eccentricity of the object’s orbital ellipse. 5. Using the scale given on each diagram, convert the centimeters (cm) to Astronomic Units (A.U.) and record that distance. 6. Use the chart below to identify the orbiting body. 7. Record your data and conclusions below: OBJECT A: Distance from center to far edge of orbit (SMA) = __________ cm ________ A.U. Distance from center to the sun = __________ cm ________ A.U. eccentricity = Average distance from sun to orbiting body = ________ A.U. The object is: OBJECT B: Distance from center to far edge of orbit (SMA) = __________ cm ________ A.U. Distance from center to the sun = __________ cm ________ A.U. eccentricity = Average distance from sun to orbiting body = ________ A.U. The object is: OBJECT C: Distance from center to far edge of orbit (SMA) = __________ cm ________ A.U. Distance from center to the sun = __________ cm ________ A.U. eccentricity = Average distance from sun to orbiting body = ________ A.U. The object is: 8. Use Kepler’s Third Law (P2 = a3) to calculate the period of orbit for each object. Object A: Object B: Object C: Based upon the orbital data, do you conclude that object A and object B follow Kepler’s Third Law? Explain your reasoning. Names: Date: Period: Recall drawing an ellipse (oval). Unlike a circle, it has different radii (measured from its center). Instead of having 1 center point, it has 2 foci. As shown here, the distance from one focus to a point on the ellipse, then back to the other focus, is the same for every point on the ellipse (in fact, that’s the definition.) As implied by Kepler’s Third Law, there are two others. The First Law addresses planetary geometry. Kepler’s First Law states that all planets follow an elliptical orbit around the sun, and the sun is one of the foci (there’s nothing at the other.) Kepler’s Second Law examines what happens as a planet changes speed during its orbit. Kepler realized that a planet will cover the same amount of area at all times. Using 2 weeks as an example, a planet will cover the same amount of area during any 2-week period, no matter where it is in its orbit. Consequently, this is sometimes also referred to as The Law of Equal Areas. (Note that this amount is unique to each planet. The area for different planets will be different in that same 2-week period.) The number of boxes between A and B is the same as between H and I. Kepler presented both these laws in 1609. It would take another decade to formulate the Third Law. Now we can summarize the three laws: Although the planets are typically illustrated as equally-spaced from the sun, their actual distance gets bigger as they get farther from the sun. NOT ALL ORBITS ARE CREATED EQUAL. ALTHOUGH THEY’RE ALL ELLIPTICAL, SOME ARE ROUNDER AND SOME ARE FLATTER. THIS ASPECT OF AN OVAL IS CALLED ITS ECCENTRICITY. THE SYMBOL IS e AND IT IS EQUAL TO HALF THE DISTANCE BETWEEN THE FOCAL POINTS DIVIDED BY THE SEMI-MAJOR AXIS. IF THE UPPER HORIZONTAL LINE IS 12 MILLION MILES LONG AND THE LOWER (SHORTER) LINE IS 9 MILLION MILES LONG, THEN THE ORBIT’S ECCENTRICITY IS EQUAL TO 9,000,000 MILES ÷ 12,000,000 MILES = 0.75 AN ECCENTRICITY MUST BE BETWEEN ZERO AND ONE. A PERFECT CIRCLE HAS AN ECCENTRICITY OF ZERO AND FOR A STRAIGHT LINE IT EQUALS 1. KNOWING A PLANET’S ORBITAL ECCENTRICITY CAN PROVIDE AN ADDITIONAL CLUE FOR IDENTIFICATION IF THE PERIOD OF ORBIT (FROM KEPLER’S 3RD LAW) IS UNKNOWN, OR VERY CLOSE TO ANOTHER PLANET’S.