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.vibration 2.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

1.What term describes the substance a wave travels through? a)vibration b)medium c)matter 2.What is the top of a wave called? a)crest b)trough c)Equilibrium point 3.If a wave oscillates twice each second, what is its period? a)2 seconds b)2 Hz c)½ second

Describing Waves 3.What is the amplitude of the wave above? a)14 cm b)12 cm c)½ second 4.What is the wavelength of the wave above? a)14 cm b)7 cm c)6 cm 5.What is the frequency of the wave above? a)14 Hz b)6 Hz c)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

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.

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.

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

Motion of Waves True 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.

Kinetic and Potential Energy 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 J b)500 J c)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 J b)10 J c)20 J

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 Potential energy 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: 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 = 1/2mv² 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

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. 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

Calculating with Conservation of Energy 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 Energy A 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 Read sections and highlight

Understanding the purpose of Beginning with Learning NAME DATE The Unit Organizer BIGGER PICTURE LAST UNIT CURRENT UNIT NEXT UNIT UNIT SELF-TEST QUESTIONS is about... UNIT RELATIONSHIPS Words to KnowUNIT MAP CURRENT UNIT Understand work and mechanical energy 2.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 engine 6.Understand how the laws of thermodynamics and entropy limit a heat engine’s performance. Compare and Contrast Explain Remember UO Vocab Lesson 4 Quiz Lesson 5 Quiz Lesson 6 Quiz 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