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TAKS Objective 5 PHYSICS General Tips for TAKS Science: • USE THE FORMULA CHART – Here’s how: • The TAKS does not expect you to know how to do every Science problem, that’s why they give you a formula chart • If you see a TAKS Science question with any numbers in it, get out the formula chart, read the question then re-read the question. Look for a formula that might go with the question. • For each number you are given, explore the words immediately around it to determine where to plug the number into the equation. Example 1: A car traveled 150 km in 2.5 hours. What was its average speed in km per hour? Record and bubble in your answer on the answer document. General Tips for TAKS Science: • DON’T FORGET THE PERIODIC TABLE – Any time you see the name of an element in a question, or a word you even suspect to be an element name, get out the periodic table – Also, get out the periodic table if you see any of the following words in a question: • • • • • • “group” “period” “atomic mass” “atomic number” “protons” “neutrons” “electrons” “valence” Example 2: According to the periodic table, which element most readily accepts electrons? A Fluorine B Nitrogen C Arsenic D Aluminum General Tips for TAKS Science • There are a lot of vocabulary words in Science, you should study vocabulary to prepare for the Science TAKS. This is especially important for Objectives 2 and 3 (BIOLOGY) • IF YOU DO NOT KNOW A WORD: – Don’t panic! Use context clues and try to figure out what the word means. – Don’t get hung up on words you don’t know. Instead, focus on the words that you DO know, and try to make sense of the rest using what you know. What does Objective 5 have in it? • Questions about the motion of objects or people. • Questions about energy and energy conservation • Questions about heating and cooling • Questions about light, sound, and waves • MOST of the math-related questions on the Science TAKS test come from Obj. 5 Motion: Time, Distance, Speed, Acceleration Time and Distance • The SI unit for time is seconds • The SI unit for distance is meters SPEED • Also known as VELOCITY • Formula: speed = distance / time • Common units: – m/s – meters per second – mi/hr – mph – miles per hour Example 3: Speed/Velocity The picture shows the position of a ball every 0.25 second on a photogram. Using a ruler, determine the velocity of the ball. F 3.5 cm/s G 10.5 cm/s H 14.0 cm/s J 28.0 cm/s Acceleration • The rate of change in speed • When an object “speeds up” that’s positive acceleration • When an object “slows down” that’s negative acceleration, or deceleration • Formula: Acceleration = final velocity – initial velocity change in time Acceleration • Common units for acceleration include: – m/s2 - “meters per second squared” – mi/hr2 – “miles per hour squared” *Generally the units for acceleration will be ______ per _______ squared. Example 4: Acceleration • What is the acceleration of a race car that speeds up from 150 mph to 200 mph over 4 seconds? A. B. C. D. -12.5 mi/hr2 12.5 mi/hr2 -5.3 mi/hr2 5.3 mi/hr2 Newton’s Laws of Motion Things keep doing what they were doing. Newton’s 1st Law: An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. Newton’s Laws of Motion The Law of Inertia in Everyday Life: – When you slam on the breaks in a car, the car begins stopping, but you and the belongings in the car keep going, that’s why you have a seatbelt. What is an unbalanced force? Balanced forces: UN-balanced forces: Newton’s Laws of Motion Newton’s Second Law: The Force Equation “The acceleration of an object is inversely proportional to its mass and directly proportional to its force.” FORMULA: F = ma “Force equals mass times acceleration” A little bit more on force: • The units for force are Newtons (N) • 1 Newton = 1 (kg*m)/s2 Example 5: Force Newton’s Laws of Motion Newton’s 3rd Law: “For every action there is an equal and opposite reaction.” For example: When you step out of a boat in the direction of the shore, the boat tends to slide backwards in the direction of the lake. Example 6: Newton’s Laws Momentum • Momentum can be defined as “mass in motion” • Momentum depends on two variables: – How much stuff is moving (mass) – How fast that stuff is moving (velocity) Formula: Momentum = mass * velocity or p = m * v Conservation of Momentum • CONSERVED = not changing or “constant” • The Law of Conservation of Momentum states: – “When two objects collide, the total momentum before the collision must equal the total momentum after the collision” Conservation of Momentum Real-life example: – If two football players, a defensive tackle, and a running back collide on the field the resulting momentum will be the same as the sum of both players’ individual momentums before the tackle takes place. Example 7: Momentum Work • “a force acting upon an object to cause a displacement” • Work is the force applied over a distance • The formula for work is: or Example 8: Work Power • Power is the rate at which work is done • The unit for power is the watt • 1 watt = 1 (N*m)/s • When we say that something is “powerful” we mean it is both STRONG and FAST Power For instance, you can pull a refrigerator box 100 meters, or you can set it in the back of a truck and let the truck carry it 100 meters. Both the truck and you could do the same amount of work, but the truck can do it much faster. The truck is more powerful. Example 9: Power Mechanical Energy • Mechanical energy is the energy an object has due to its motion (kinetic) or its stored energy of position (potential) Conservation of Energy • Remember that “conserve” means “to not change” or “to keep constant” • The Law of Conservation of Energy states that energy can be neither created, nor destroyed • In other words, energy doesn’t disappear, it just changes forms. When you hold a book up in the air, it has potential energy. When you drop the book, as it falls it has kinetic energy. The potential energy wasn’t destroyed, it just got changed into kinetic energy. Example 10: Energy Different Forms of Energy • There are many forms of energy. Some examples are: – – – – – Chemical (stored) Gravitational potential energy (stored) Thermal energy (kinetic) Sound energy Solar energy Example 11: Energy Machines • Machines are used to change a small force into a larger one, change direction of the force to make it more useful • Simple machines: levers, ramps, wheels, pulleys and screws • Complex machines are made up of several or many simple machines • Mechanical advantage: the amount by which a machine multiplies the force Example 12: Mechanical Advantage Efficiency • Machines are not 100% efficient so some work done is lost to things like friction. • The work you put in to a machine is called “work input” • The work the machine actually does is called “work output” Example 13: Efficiency WAVES WAVES • There are many different kinds of waves. A few examples are: – Sound waves, visible light waves,radio waves, microwaves, water waves, sine waves, cosine waves, telephone chord waves, stadium waves, earthquake waves, waves on a string, and slinky waves • On a molecular level, waves are disturbances that travel through a medium (for instance air) via one molecule bumping into and vibrating the next The Parts of a Wave Amplitude Period and Frequency of Waves • The period of a wave is the time it takes for one point on the wave to go through one vibration. In other words, to go from rest to crest to trough and back to crest. • The units for period are seconds (s) • The frequency of a wave is the number of vibrations that occur per second • The units for frequency are Hertz (Hz) Wave Velocity • The velocity of a wave can be found by multiplying the frequency by the wavelength. Example 14: Wave Velocity Interference • When two waves collide, they either add to one another, or cancel each other out • Waves intersecting or colliding is called “interference” Destructive Constructive Light • Light travels on electromagnetic waves • There are wavelengths of light that humans can see, and wavelengths that we can’t. The wavelengths we can see are referred to as the visible light spectrum. Light • You learned in biology that plants contain a green pigment called chlorophyll. Plant leaves appear green to the human eye because they reflect green light –all of the other colors are absorbed. • General rule: Objects appear to be the color that they reflect, not the colors they absorb Example 15: Color Light • Certain smooth surfaces will reflect light (like mirrors, or the surface of a pond) • Sometimes light waves will move from one medium into another, like moving from the air into water. When light crosses a boundary such as that between air and water, the light wave gets refracted, or “bent” Light • Surfaces that are not smooth will not reflect light in a consistent or predictable manner. Instead they cause the light to be dispersed into all different directions • For instance, if you shine a light on a mirror, you see the beam come back off of the mirror. However, if you shine a light on a sweater you will not see a reflected beam. The uneven surface of the sweater will cause the light to be dispersed. Example 16: Light Sound •Sound travels on waves that are interpreted by the inner ear •Vibrations disrupt air molecules around the source of the vibration, causing sound •The pitch of the sound heard is determined by the frequency of the vibrations (i.e. faster vibration = higher frequency = higher pitch) Example 17: Sound Heat Energy Transfer Heat Transfer • Thermal energy, or heat energy, is the result of particles of matter moving (remember kinetic energy?) • Heat energy can be transferred from one medium to another in three main ways: – Conduction – Convection – Radiation Conduction • In the process of conduction, heat moves through a substance or from one substance to another by the direct contact of molecules • Here’s how it works: Fast moving molecules collide with slow moving molecules. This causes the slow moving molecules to move faster. Now, these molecules collide with other slow moving molecules causing them to move faster. This process is repeated over and over. In this way heat energy is transferred from molecule to molecule all the way through a substance. Conduction • Some substances conduct heat better than others. These are referred to as conductors. • Substances that do NOT conduct heat well are known as insulators. • For example: The reason wooden spoons are used when cooking instead of metal spoons is because the wooden spoons are good insulators. Because metal spoons are good conductors they heat up quickly and can easily burn their users. Convection • Warm air rises. Cool air sinks. When gases or liquids warm up they transfer the heat upward and outward from their sources. Radiation • Radiation is the transfer of energy by electromagnetic waves • Examples: – Feeling the sun on your face – Feeling the warmth of a campfire while sitting around the campfire Convection, Conduction, and Radiation Example 18: Heating and Cooling