unit 3 sound and light. vibration a shaking that can be described using a wave, such as an...

Unit 3

Sound and Light

vibration

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

wave

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

medium

• The substance through which a wave travels

crest

• The top of a wave

trough

• The bottom of a wave

Equilibrium point

• The moment at which opposing forces cancel each other out

amplitude

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

Wave length

• The distance between one crest and the next

frequency

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

hertz

• The unit used to measure frequency

period

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

Describing Waves

• Ways to describe waves:1. vibration2. 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

Describing Waves

• Ways to describe waves:– Crest– Trough– Equilibrium point– Amplitude– wavelength

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)

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.

Describing Waves

1. What term describes the substance a wave travels through?

a) vibrationb) mediumc) matter

2. What is the top of a wave called?a) crestb) troughc) Equilibrium point

3. If a wave oscillates twice each second, what is its period?a) 2 secondsb) 2 Hzc) ½ second

Describing Waves

3. What is the amplitude of the wave above?a) 14 cmb) 12 cmc) ½ second

4. What is the wavelength of the wave above?a) 14 cmb) 7 cmc) 6 cm

5. What is the frequency of the wave above?a) 14 Hzb) 6 Hzc) 1Hz

6 cm

14cm

1 second

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

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

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


• 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.


• 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.


• 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

Motion of WavesTrue or False:1. In a transverse wave, the medium vibrates in the same direction that the

wave moves.2. Ocean waves are transverse waves.3. A wave with a high frequency vibrates very quickly.4. By shaking a rope faster, you can make the waves move down the rope

more quickly.5. In order to change the speed of a wave, you must change something

about the medium.6. Diffraction is the process in which waves spread out as they pass through

an opening.7. The larger the opening a wave passes through, the more the wave will

diffract.8. Waves that are matched crest to crest and trough to trough are called

“out of phase”.9. When two waves interfere destructively, they stop moving completely.


9. 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

a) 400 Jb) 500 Jc) 5000 J

10. 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?

a) 2 Jb) 10 Jc) 20 J

B

A

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

Conservation of Energy

�⃰ Energy cannot be created or destroyed• Conservation of Energy:

‒ amount of energy does not change but it can change forms

Potentialenergy

Kinetic energy

Potential energy

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

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


• Ex: An archer releases an arrow that has a mass of .1 kg into a target. The arrow is moving at 30 m/sec.1. How much kinetic energy does the arrow have?• KE = 1/2m•v²• KE = ½(.1kg) •(30m/sec) ²• KE = .05kg • (900m ²/sec ²)• KE = 45 J

2. 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


• Ex: An archer releases an arrow that has a mass of .1 kg into a target. The arrow is moving at 30 m/sec.3. 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


A wagon with a mass of 20kg is moving with a speed of 5 m/s.1. How much kinetic energy does it have?

2. How much work was done to give it this energy?

3. 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)

Calculating with Conservation of EnergyA boy is jumping on a pogo stick. His eight is 500N, and he jumps 0.3 m.4. How much gravitational potential energy does

he have at the top of his jump? (PE =Fd)

5. How much work can he do to compress the pogo stick’s spring when he lands?

6. If it takes an average force of 750 N to compress the spring, how far will the spring compress?

Temperature and Heat

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Understanding the purpose of

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CURRENT UNIT1 32

4

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1. Understand work and mechanical energy2. Apply the principle of the conservation of energy.3. Understand the physical meaning of temperature and heat.4. Explain the effect of temperature and heat on objects.5. Understand the functioning of a heat engine6. Understand how the laws of thermodynamics and entropy limit a heat engine’s

performance.

Compare and Contrast

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Remember

UO Vocab

Lesson 4 Quiz

Lesson 5 Quiz

Lesson 6 Quiz

12/2

12/2

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

unit 3 sound and light. vibration a shaking that can be described using a wave, such as an...

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