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Transcript
Do Now What is motion? Objective Students will be able to analyze and integrate information in order to demonstrate knowledge of how to measure motion. Agenda Do Now Motion, Speed, Velocity, Acceleration Expectations Lab Motion and Speed Motion – an object’s change in position relative to a reference point Speed – the distance traveled divided by the time interval during which the motion occurred 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑝𝑒𝑒𝑑 = 𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒 Imagine that two birds leave the same tree at the same time. They both fly at 10 km/h for 5 min, 12 km/h for 8 min, and 5 km/h for 10 min. Why don’t they end up at the same place? Velocity and Acceleration Velocity – the speed of an object in a particular direction Acceleration – the rate at which velocity changes over time; an object accelerates if its speed, direction, or both change 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑎𝑐𝑐𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 = 𝑓𝑖𝑛𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 −𝑠𝑡𝑎𝑟𝑡𝑖𝑛𝑔 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑡𝑖𝑚𝑒 𝑖𝑡 𝑡𝑎𝑘𝑒𝑠 𝑡𝑜 𝑐ℎ𝑎𝑛𝑔𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 Expectations Lab will be collected at the end of class Work in groups of 4 If you are not completing the lab appropriately, you will receive a 0 as a lab grade Raise your hand if you do not what to do Variables Independent: the variable that does not change Dependent: the variable that changes Control: the standard variable (beginning) Procedure Mark the floor with tape from 0 cm, 50 cm, 100 cm, and 150 cm Set up your ramp using text books Follow Step 3 from Procedure and follow the directions Do Now What is friction? Objective Students will be able to analyze and integrate information in order to explain why friction occurs. Agenda Do Now Friction Lab/Directed Reading While playing ball, your friend throws the ball out of your reach. Rather than running for the ball, you walk after it. You know that the ball will stop. But do you know why? Friction: a force that opposes motion between two surfaces that are in contact. The source of friction Friction occurs because the surface of any object is rough. ◦The hills and valleys of one surface stick to the hills and valleys of the other surface. Two factors that effect the amount of friction between two surfaces: ◦The force pushing the surfaces together ◦The roughness of the surfaces The Effect of Force on Friction If the force pushing or pulling the surfaces of two objects increases, the hills and valleys can come into closer contact creating more friction. ◦Ex. Slide hand across desk. Then push down and slide hand across desk. Objects that weigh less exert less downward force than objects that weigh more do. But changing how much of the surfaces come in contact does not change the amount of friction. The Effect of Rougher Surfaces on Friction Rough surfaces have more microscopic hills and valleys than smooth surfaces do. So the rougher the surface is, the greater the friction is. ◦Ex. A ball rolling across grass compared to a puck on the ice. Types of Friction There are two types of friction: ◦Kinetic Friction: Friction between moving surfaces. ◦Kinetic means “moving” ◦Static Friction: When a force is applied to an object but does not cause the object to move. ◦Static means “not moving” Types of Friction Two types of kinetic friction: ◦Rolling ◦Takes less force to roll an object than to slide it. ◦Ex. Anything that has wheels uses rolling kinetic friction ◦Sliding ◦Takes more force to slide an object than to roll it ◦Ex. Applying brakes to a bicycle, writing with a pencil, scratching an itch Friction: Harmful and Helpful Think about how friction affects a car. Without friction, the tires could not push against the ground and move the car forward, and the brakes could not stop the car. Without friction, a car is useless. Friction: Harmful and Helpful Friction: ◦Can cause holes in your socks and in the knees of your jeans ◦Can cause erosion of topsoil that nourishes plants through wind and water ◦Allows you to write ◦Allows you to walk without slipping and falling Sometimes it is necessary to decrease or increase friction. Some Ways to Reduce Friction Lubricants: substances that are applied to surfaces to reduce the friction between the surfaces. ◦Ex. Motor oil, wax and grease. ◦Lubricants are usually liquids but they can be solids or gasses. Friction can be reduced by switching from sliding kinetic friction to rolling kinetic friction. Friction can also be reduced by making a surface smoother. Ex. Sanding a wooden bench. Some Ways to Increase Friction Make surfaces rougher. ◦Sand scattered on icy roads ◦Textured batting gloves. Increase the force pushing the surfaces together. ◦Sanding a piece of wood works faster if more force is applied. ◦Cleaning a dirty dish using a sponge Do Now Why is friction helpful? Objective Students will be able to analyze and integrate information in order to explain why friction occurs. Agenda Do Now Review Friction Lab/Directed Reading/Section Review Group Work Directed Reading Complete the directed reading activity with your group. Will be collected at the end of the lab Section Review Page 19 Lab Follow the directions from the procedure Use three books (2 for the base, 1 for the incline plane) Use the toy car to measure the distance In your own words, write a definition for the term net force. A combination of all forces that act on an object. In your own words, write a definition for the term friction. Friction is a force between any two surfaces, that opposes motion. This type of force causes a change in the speed or direction of an object. Unbalanced force Which direction is the force of friction pushing against the block? Why is it easier to slip when there is water on the floor? a) The water is a lubricant that when spilled, fills in the hills and valleys on the floor and reduces friction between your feet and the floor Forces are measured in these units. Newtons Explain why friction occurs. Friction occurs because surfaces are covered with microscopic “hills and valleys” that stick to each other when they come in contact. Friction is caused when microscopic hills and valleys of objects rub together: How does the roughness of surfaces that are touching affect the friction between surfaces? Rough Surfaces have more hills and valleys that increase the force of friction. Smooth surfaces have less hills and valleys, therefore less friction occurs. Which will have more friction? These surfaces will have more friction because they have larger hills and valleys than the other picture. This means they are more rough. Describe how the amount of force pushing two surfaces together affects friction. If the force pushing the two surfaces together is great, the hills and valleys are in closer contact and friction increases. More Force = More Friction Name two ways in which friction can be increased. Make a surface rougher Push surfaces together harder List the two types of friction, and give an example of each. Kinetic- sliding a book across the tabletop Static- pushing a piece of furniture and it not moving. List the three types of Kinetic Friction and give an example of each: Sliding Kinetic Friction- moving a book across a desk, applying brakes in a car, scratching your arm Rolling Kinetic Friction- wheels of a bike, toy car, trains on a track Fluid Kinetic Friction- oil lubricating parts on a plane, car, or bike, water flowing through a hose Forces Two young girls are fighting over a present. One is pushing is with a force of 10N to the right and the other is pushing with a force of 50 N to the left. Use the picture below to answer the questions that follow. 1.The forces shown above are PUSHING / PULLING/ PUSHING AND PULLING forces. 2. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES. 3. The forces are EQUAL / NOT EQUAL. 4. The forces DO / DO NOT balance each other. 5. There IS / IS NO motion. 6. The net force is __________________ in _________________ (direction). Forces Two children are moving their wagon across the street. One is pulling the wagon to the left with a force of 100N and the other is pushing the wagon with a force of 100 N to the left. Use the picture below to answer the questions that follow. 1.The forces shown above are PUSHING / PULLING/ PUSHING AND PULLING forces. 2. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES. 3. The forces are EQUAL / NOT EQUAL. 4. The forces DO / DO NOT balance each other. 5. There IS / IS NO motion. 6. The net force is __________________ in _________________ (direction). Friction Force that opposes motion between 2 surfaces Depends on the: ■ types of surfaces ■ force between the surfaces Types of Friction ■ Static Friction: (Couch Potato) – Force between objects at rest ■ Sliding Friction: (Ice skating) – Solid surfaces slide over each other ■ Rolling Friction: (Rollerblading) – An object rolls over a surface. ■ Fluid friction: (Submarine) – An object moves through a fluid Types of Friction There are two types of friction: ◦Kinetic Friction: Friction between moving surfaces. ◦Kinetic means “moving” ◦Static Friction: When a force is applied to an object but does not cause the object to move. ◦Static means “not moving” Types of Friction Two types of kinetic friction: ◦Rolling ◦Takes less force to roll an object than to slide it. ◦Ex. Anything that has wheels uses rolling kinetic friction ◦Sliding ◦Takes more force to slide an object than to roll it ◦Ex. Applying breaks to a bicycle, writing with a pencil, scratching an itch Friction Friction is greater... – between rough surfaces – when there’s greater force between surfaces (such as more weight) Lubricant Changes sliding friction into fluid friction Friction Is friction always bad? Do Now What is gravity? Objective Students will be able to utilize information from friction in order to describe gravity and its properties. Agenda Do Now Test Next Friday (5/13) Collect Do Nows Friction Video Gravity Reminders for those going on class trip… ARRIVE AT SCHOOL AT 7 AM Shorts fingertip length Money for dinner Wear comfortable clothes What causes friction? Question: Have you ever seen a video of astronauts on the moon? They bounce around like beach balls even though they wear big, bulky spacesuits. Why is leaping on the moon easier than leaping on earth? Gravity: the force of attraction between objects that is due to their masses. ◦The force of gravity can change the motion of an object by changing it’s speed, direction or both. There is less gravity on the moon. The Effects of Gravity on Matter Remember: All matter has mass. Gravity is a result of mass. Therefore, matter is affected by gravity. Because all matter is affected by gravity, that means all objects experience an attraction toward all other objects. ◦Right now, because of gravity, you are being pulled toward your book, your pencil, and every other object around you. They are also being pulled toward one another. Why don’t you feel gravitational pull towards all objects around you? The reason you don’t feel the attraction between you and all other objects around you is that the mass of most objects is too small to cause a force large enough to move objects toward each other. The earth is what causes those objects to seem like they have no attraction to you at all. The size of Earth’s gravitational force Compared with all objects around you, Earth has a huge mass. Therefore, Earth’s gravitational force is very large. You must apply forces to overcome Earth’s gravitational force any time you lift objects or even parts of your body. Earth’s gravitational force pulls everything toward the center of Earth. This is why objects that are dropped fall to the ground instead of moving together or toward you. Friction How do we experience friction? Newton and the Study of Gravity It has been widely recognized that Isaac Newton answered the following two questions (questions that hadn’t been answered up until this time) while watching an apple drop: ◦Why do objects fall toward Earth? ◦What keeps the planets moving in the sky? The Core of Newton’s Idea Newton knew that unbalanced forces are needed to change the motion of objects. He concluded that an unbalanced force on the apple made the apple fall. From this he reasoned that an unbalanced force on the moon kept the moon moving circularly around Earth. He proposed that these two forces are actually the same force, the force of attraction called “gravity.” The Birth of a Law Newton summarized his ideas about gravity in a law now known as the “law of universal gravitation.” ◦This law describes the relationships between gravitational force, mass, and distance. ◦The law is “universal” because it applies to all objects in the universe. The Law of Universal Gravitation All objects in the universe attract each other through gravitational force. The size of the force depends on: ◦ the masses of the objects ◦ the distance between the objects. Gravitational Force Increases as Mass Increases The cat and the elephant: ◦The elephant has a larger mass than the cat. Therefore, the amount of gravity between the elephant and the earth is greater than the cat and the earth. ◦Because of the effect of gravity on their masses, the cat is much easier to pick up. ◦There is also gravitational pull between the cat and the elephant, but the mass of the elephant is so much smaller than the earth’s mass, their gravitational pull is much smaller. Gravitational Force Increases as Mass Increases This phenomena shows why astronauts bounce on the moon and not on earth. The moon’s mass is much less than earth’s mass so it’s gravitational pull is much less allowing the astronauts to bounce more. Gravitational Force Decreases as Distance Increases You jump up and land on the ground because of the gravitational force between you and earth. The sun is 300,000 times more massive than earth… so why doesn’t the sun’s gravitational force affect you more than earth’s does? The reason is that the sun is so far away. ◦We are about 150 million kilometers away from the sun. If you could stand on it, you would find it impossible to move AT ALL. Weight as a Measure of Gravitational Force Gravity is a force of attraction between objects. Weight: is a measure of the gravitational force on an object. ◦Usually you hear weight referring to the Earth’s gravitational pull on an object, but weight can also be a measure of the gravitational force exerted on objects by the moon or other planets. Is there a difference? Is there a difference between mass and weight? The Differences Between Weight and Mass Weight is related to mass, but they are not the same. ◦Weight changes when gravitational force changes. Mass: the amount of matter in an object. ◦The amount of mass in an object does not change. This can get confusing… because weight and mass are “constant” on Earth, the terms weight and mass are often used to mean the same thing. Be sure you know the difference!!! Units of Weight and Mass You have learned that the SI unit of force is a Newton (N). Gravity is a force, and weight is a measure of gravity. So… weight is also measured in Newtons (n). The SI unit of mass is the kilogram (kg). Mass is often measured in grams and milligrams as well. On earth, a 100g object, such as an apple weighs about 1 N. Why Bathroom Scales Confuse Us When you use a bathroom scale, you are measuring the gravitational force between your body and Earth. So you are measuring your weight, which should be given in Newtons. However, many bathroom scales have units of pounds and kilograms instead of Newtons. Thus, people sometimes mistakenly think that the kilogram (like the pound) is a unit of weight. Exit Slip Why is it harder to pick up an 18 lb. bowling ball as opposed to a baseball? Do Now What is the difference between mass and weight? Objective Students will be able to analyze and integrate information in order to explain the law of universal gravitation. Agenda Do Now Test this Friday Interim Reports Next Week Video and Worksheet Do Now What is the law of universal gravitation? Objective Students will be able to analyze and integrate information in order to explain the law of universal gravitation. Agenda Do Now Test Friday Interim Reports Next Week Expectations Webquest Expectations Do not go on websites other than the one you are supposed to be on If caught, you will get point deductions, NO COMPROMISES If you get 3 point deductions, you receive a 0 Work in pairs only, with the pair you are seated with, no exceptions Do Now Does the gravitational force change with altitude? Objective Students will be able to analyze and integrate information in order to demonstrate knowledge of matter in motion. Agenda Do Now Test Friday Interim Report Next Week Finish Gravity Review Game/Chapter Review Expectations If you need anything, raise your hand Do not get out of your seat Do not tap your tap or pencils Do not call out “Mr. Han” to get my attention, I will get to you in the order I see your hands Point deductions will be given if you are not following the expectations Gravitational Force Decreases as Distance Increases You jump up and land on the ground because of the gravitational force between you and earth. The sun is 300,000 times more massive than earth… so why doesn’t the sun’s gravitational force affect you more than earth’s does? The reason is that the sun is so far away. ◦We are about 150 million kilometers away from the sun. If you could stand on it, you would find it impossible to move AT ALL. Weight as a Measure of Gravitational Force Gravity is a force of attraction between objects. Weight: is a measure of the gravitational force on an object. ◦Usually you hear weight referring to the Earth’s gravitational pull on an object, but weight can also be a measure of the gravitational force exerted on objects by the moon or other planets. Is there a difference? Is there a difference between mass and weight? The Differences Between Weight and Mass Weight is related to mass, but they are not the same. ◦Weight changes when gravitational force changes. Mass: the amount of matter in an object. ◦The amount of mass in an object does not change. This can get confusing… because weight and mass are “constant” on Earth, the terms weight and mass are often used to mean the same thing. Be sure you know the difference!!! Units of Weight and Mass You have learned that the SI unit of force is a Newton (N). Gravity is a force, and weight is a measure of gravity. So… weight is also measured in Newtons (n). The SI unit of mass is the kilogram (kg). Mass is often measured in grams and milligrams as well. On earth, a 100g object, such as an apple weighs about 1 N. Why Bathroom Scales Confuse Us When you use a bathroom scale, you are measuring the gravitational force between your body and Earth. So you are measuring your weight, which should be given in Newtons. However, many bathroom scales have units of pounds and kilograms instead of Newtons. Thus, people sometimes mistakenly think that the kilogram (like the pound) is a unit of weight. Do Now A car is moving downwards with a velocity of 5 m/s downhill and changes to 7 m/s downhill. How do you know that the hiker has a positive acceleration? Objective Students will be able to analyze and integrate information in order to demonstrate knowledge of matter in motion. Agenda Do Now Collect Do Nows Review/Prep. Test Expectations If you need anything, raise your hand Do not get out of your seat Do not tap your tap or pencils Do not call out “Mr. Han” to get my attention, I will get to you in the order I see your hands Point deductions will be given if you are not following the expectations