1. WAVES
Physics

2. Waves transmit ENERGY from one place to another.
If you can only remember one thing…
The source of all waves is something that vibrates.
Waves transmit ENERGY from one place to another.

3. Simple Harmonic Motion
Simple Harmonic Motion (SHM) – Back and forth oscillatory motion.
Ex: Pendulums, Springs
Motion looks like a sine curve.

4. Parts of a Wave
CREST
TROUGH

5. Wave Description Crest – high point on a wave
Trough – low point on a wave
Amplitude (A) – the distance from the midpoint to the crest
Wavelength (λ)– the distance from the top of one crest to the top of the next one (or between successive identical parts of the wave)
Frequency (f)– number of vibrations an object makes per second, units are in Hertz (Hz = 1 cycle/second)
Period (T) – number of seconds it takes to go through one vibration

6. Frequency and Period
Frequency (f) and period (T) are reciprocals of each other.
Ex: If the frequency of a wave is 4 Hz, what is its period?

7. Wave Motion
Most of the information around us gets to us in some form of wave.
Sound is energy that travels to our ears in the form of one kind of wave.
Light is energy that comes to our eyes in the form of a different kind of wave.
The signals that reach our radios and TVs also travel as waves.

8. Wave Motion
When energy is transferred by a wave from a vibrating source to a distant receiver, there is no transfer of matter between the two points!
The energy transferred from a vibrating source to a receiver is carried by a disturbance in a medium, not by matter moving from one place to another within the medium.

9. Shallow Water Wave

10. A circular water wave in a still pond moves out from the center in an expanding circle.

11. Wave speed = wavelength X frequency
The speed of a wave depends on the medium through which it travels.
Whatever the medium, the speed, wavelength, and frequency of the wave are related
Wave speed = wavelength X frequency
[m/s] = [m] x [Hz]
Sound waves move at speeds of about m/s in air and four times faster in water.

12. Checking for Understanding:
Complete the following table:

13. Transverse Waves
Transverse Waves – the motion of the medium is at right angles to the direction in which the wave travels
Examples: stretched strings in musical instruments, waves on surfaces of liquids, radio waves, light waves, and s-waves (earthquakes)

14. Example Problem
The water waves below are traveling with a speed of 2 m/s and splashing periodically against the Wilbert's perch. Each adjacent crest is 4 meters apart and splashes Wilbert’s feet upon reaching his perch. How much time passes between each successive drenching?

16. Longitudinal Waves
Longitudinal Waves – particles move along the direction of the wave
Examples: sound waves and p-waves (earthquakes)

18. Interference
Interference Pattern – arrangement of places where wave effects are increased, decreased, or neutralized

19. Interference
Constructive Interference (reinforcement) – the crest of one wave overlaps the crest of another, their individual effects add together producing an increased amplitude
Destructive Interference (cancellation) – the crest of one wave overlaps the trough of another, their individual effects are reduced

21. Standing Waves
Standing Wave – certain parts of the wave remain stationary, when the incident wave and reflected wave meet
Nodes – part of the standing wave which does not move and has no amplitude (at equilibrium)
Antinodes – position on a standing wave which has the largest amplitude

22. Standing Wave

23. SOUND
Physics

24. Sound All sounds originate in the vibrations of material objects.
Sound is a longitudinal wave.
A pulse of compressed air is called a compression.
A pulse of low-pressure air is called a rarefaction.
Rarefaction
Compression

25. Sound Sound travels in solids, liquids, and gases.
The speed of sound differs in different materials.
In generally, sound is transmitted faster in liquids than in gases, and still faster in solids.
Sound cannot travel in a vacuum.
The speed of sound in dry air = m/s.

26. Loudness
Loudness is a psychological sensation sensed in the brain, and it differs for different people.
Loudness varies as the logarithm of intensity (wave energy).
(ex: An increase from 10 dB to 20 dB means the sound is 10 times louder).
The unit of intensity for sound is the decibel (dB), named after Alexander Graham Bell.

27. Natural Frequency & Resonance
When an object is disturbed, it vibrates at its own special set of frequencies, which make a certain sound.
The natural frequency of an object depends on the elasticity and shape of the object.
When an object vibrates at its natural frequency, it uses the least amount of energy.
Resonance - When the forced vibration on an object matches its natural frequency, an increase in amplitude occurs.

28. Natural Frequency & Resonance

29. Interference and Beats
When constructive interference occurs with sound waves, the listener hears a louder sound.
When destructive interference occurs, the listener hears a fainter sound or no sound at all.
Noise-cancelling headphones
When two tones of slightly different frequency are sounded together, a regular fluctuation in the loudness of the combined sounds is heard.
The periodic variation in the loudness of sound is called beats.
Beats can be heard when slightly mismatched tuning forks are sounded together. When the combined waves reach your ears in step, the sound is a maximum. When the forks are out of step, in the sound is a minimum.

30. Interference

31. The Doppler Effect
Doppler Effect – The apparent change in frequency of a wave due to the motion of the source or the observer.
As a wave source approaches, an observer encounters waves at a higher frequency. As the wave source moves away, an observer encounters waves with a lower frequency.
Ex: Ambulance siren passing you.

32. Doppler Effect Formula
f = actual frequency [Hz]
f’ = apparent frequency [Hz]
v = wave speed [m/s] (for sound this is 330 m/s)
v0 = observer speed [m/s]
vs = source speed

33. Doppler Possibilities
**Source moving away from observer (+)
Source moving toward observer (-)
**Observer moving towards source (+)
Observer moving away from source (-)

34. Doppler Example 1
A police car, whose siren has frequency 1080 Hz, is traveling at 30 m/s. We are traveling at 50 m/s away from the police as he chases us. Find the frequency which we hear.

35. Doppler Example 2
Sitting on the beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of the airplanes leaving JFK. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies toward her at a speed of 100 m/s?

36. Springs & Pendulums