Unit 3

1. Unit 3 Sound and Light

2. vibration • A shaking that can be described using a wave, such as an earthquake or a sound

3. wave • A repeating pattern that travels through a medium (except for light, which can travel without a medium)

4. medium • The substance through which a wave travels

5. crest • The top of a wave

6. trough • The bottom of a wave

7. Equilibrium point • The moment at which opposing forces cancel each other out

8. amplitude • The maximum distance between the center point on a wave and the trough or crest

9. Wave length • The distance between one crest and the next

10. frequency • The number of waves that pass a particular position in a certain amount of time

11. hertz • The unit used to measure frequency

12. period • The time it takes for one total oscillation of a wave

13. Describing Waves • Ways to describe waves: • vibration • Wave • Vibration travels without any material moving along with it • When you speak, the air that comes out of your mouth does not travel into other people’s ears – only the vibration of the air molecules

14. Describing Waves • Ways to describe waves: • Crest • Trough • Equilibrium point • Amplitude • wavelength

15. Describing Waves • Measuring Waves: • Wavelength and amplitude are distances so they are measured in the same units as length (m) • Frequency: how quickly waves or vibrations oscillate (move back and forth) is measured in hertz (Hz) • Period: the length of time it takes for one wave to complete is measured in time (seconds)

16. Describing Waves • Relationship between frequency and period: • Inverse or opposites • If a wave has a high frequency, then each wave does not take much time (short period) • If each wave takes a long time (long period), then there will not be that many of them each second (low frequency) Frequency = Period = For example: If the frequency of a wave is 5Hz (5 waves each second), then each wave takes econd, making the period second.

17. Describing Waves • What term describes the substance a wave travels through? • vibration • medium • matter • What is the top of a wave called? • crest • trough • Equilibrium point • If a wave oscillates twice each second, what is its period? • 2 seconds • 2 Hz • ½ second

18. Describing Waves 14cm 6 cm • What is the amplitude of the wave above? • 14 cm • 12 cm • ½ second • What is the wavelength of the wave above? • 14 cm • 7 cm • 6 cm • What is the frequency of the wave above? • 14 Hz • 6 Hz • 1Hz 1 second

19. Motion of Waves • Transverse wave: • The medium vibrates in a different direction than the waves travel • Ex: water waves wiggle up and down but the waves spread out across the surface • Ex: shaking a rope up and down but the wave moves horizontally

20. Waves of Motion • Longitudinal wave: • The vibration of the medium is in the same direction as the wave is traveling • Ex: pushing a coiled spring back and forth – vibration and wave move in the same direction

21. Kinetic and Potential Energy • Potential Energy: • Stored energy • Can be difficult to measure because you cannot see potential energy like you can see kinetic energy • Ex: when you compress a spring, stretch a rubber band, or pull back on a bow and arrow • Known as elastic potential energy • Ex: you can store energy in an object when you lift it – a hammer • Known as gravitational potential energy

22. Kinetic and Potential Energy • Potential energy can be measured but you have to know how much work was done to store the energy. • Ex: You have to do work to pull back on a bow and arrow, the more work you do to store the energy, the more energy is stored • You can calculate the amount of potential energy in an object by calculating the amount of work done to store the energy.

23. Kinetic and Potential Energy • Ex: It requires an average force of 50 N to pull back a bowstring. You pull it back .25m. How much potential energy does the bowstring have? • W = Fd • W = 50 N x .25m • W = 12.5 J • You did 12.5J of work to pull back the bowstring. So it has 12.5 of elastic potential energy.

24. Kinetic and Potential Energy • Ex: How much gravitational potential energy is in a 100N bowling ball that is 2 meters above the ground? • W = Fd • W = 100N x 2m • W = 200J

25. Motion of Waves True or False: • In a transverse wave, the medium vibrates in the same direction that the wave moves. • Ocean waves are transverse waves. • A wave with a high frequency vibrates very quickly. • By shaking a rope faster, you can make the waves move down the rope more quickly. • In order to change the speed of a wave, you must change something about the medium. • Diffraction is the process in which waves spread out as they pass through an opening. • The larger the opening a wave passes through, the more the wave will diffract. • Waves that are matched crest to crest and trough to trough are called “out of phase”. • When two waves interfere destructively, they stop moving completely.

26. Kinetic and Potential Energy • If a boy has a mass of 40 kg, and he is running at 5 m/sec, how much kinetic energy does he have? K = ½ m • v² • 400 J • 500 J • 5000 J • In stretching a rubber band, a person applies 20 N of force over a distance of 0.1 meters. How much potential energy is stored in the rubber band? • 2 J • 10 J • 20 J B A

27. Conservation of Energy • Conservation Law: • A quantity of something never changes • Ex: cutting a piece of wood; amount of matter does not change • Conservation of Matter: • Amount of matter does not change; only the shape

28. Conservation of Energy • Energy cannot be created or destroyed • Conservation of Energy: • amount of energy does not change but it can change forms Potential energy Potential energy Kinetic energy

29. Calculating with Conservation of Energy • A powerful tool to help make predictions. • If you know how much energy there is before something happens then you know how much there will be after it happens. • Ex: bowstring

30. Calculating with Conservation of Energy • Ex: A juggler throws a ball that weighs 60 N directly upwards. The ball is thrown fast enough so that it has 300 J of energy. How high will it go? • PE = Fd • PE = potential energy, F = force, d = distance • 300 J = 60 N x d • = d • 5m = d - the ball will rise 5 meters

31. Calculating with Conservation of Energy • Ex: An archer releases an arrow that has a mass of .1 kg into a target. The arrow is moving at 30 m/sec. • How much kinetic energy does the arrow have? • KE = 1/2m•v² • KE = ½(.1kg)•(30m/sec) ² • KE = .05kg • (900m ²/sec²) • KE = 45 J • How much work can the arrow do when it hits the target? • The arrow can use all 45 J of kinetic energy to push its way into the target

32. Calculating with Conservation of Energy • Ex: An archer releases an arrow that has a mass of .1 kg into a target. The arrow is moving at 30 m/sec. • If it requires 225 N to push through the target, how far into the target will the arrow go? • The arrow can do 45 J of work, so you can use the equation for work to determine what distance it moves. • W = Fd • 45J = 225 N x d • d = .2m - it will go 0.2m into the target

33. Calculating with Conservation of Energy A wagon with a mass of 20kg is moving with a speed of 5 m/s. • How much kinetic energy does it have? • How much work was done to give it this energy? • If the wagon was pushed for 10m, with how much force did it need to be pushed to give it his energy? (Hint: use the work equation)

34. Calculating with Conservation of Energy A boy is jumping on a pogo stick. His eight is 500N, and he jumps 0.3 m. • How much gravitational potential energy does he have at the top of his jump? (PE =Fd) • How much work can he do to compress the pogo stick’s spring when he lands? • If it takes an average force of 750 N to compress the spring, how far will the spring compress?

35. Temperature and Heat • Read sections and highlight

36. NAME The Unit Organizer 4 BIGGER PICTURE DATE NEXT UNIT LAST UNIT 2 3 CURRENT UNIT CURRENT UNIT 1 8 Words to Know UNIT MAP is about... 5 12/2 UO Vocab 12/2 Beginning with Lesson 4 Quiz Understanding the purpose of Lesson 5 Quiz Lesson 6 Quiz Learning • Understand work and mechanical energy • Apply the principle of the conservation of energy. • Understand the physical meaning of temperature and heat. • Explain the effect of temperature and heat on objects. • Understand the functioning of a heat engine • Understand how the laws of thermodynamics and entropy limit a heat engine’s performance. 6 Explain UNIT SELF-TEST QUESTIONS Compare and Contrast RELATIONSHIPS UNIT Remember 7

37. Unit 2 – Lesson 4 Vocabulary • energy: the ability to do work • work: how much effect a force has in causing an object to move • joules: when you multiply newtons and meters, used to measure work and energy • kinetic energy: the energy of an object that is moving • potential energy: stored energy • elastic potential energy: the potential energy of something that is stretched or compressed (spring) • gravitational potential energy: The energy stored in an object when you lift it up against gravity • conservation of matter: the amount of matter in any system remains the same, even though it may have gone through a physical or chemical change • conservation of energy: the amount of energy in any system remains the same, even if the form of the energy changes