1. Waves & Sound
Unit 6

2. rhythmic disturbances that carry energy through matter or space
Waves
Waves
rhythmic disturbances that carry energy through matter or space
All waves carry energy without transporting matter from place to place.
Molecules pass energy along to neighbor molecules (and so on)
All waves are produced by vibrations
Waves will travel as long as there is energy to carry.

3. Waves transfer energy not matter
Waves transfer energy not matter. The water waves below are carrying energy but are not moving.
Waves can only exist as they have energy to carry.

4. Mechanical Waves
Mechanical Waves: waves that can only travel through a medium
Examples: Water and sound both require air or seismic waves require earth.
Medium
material through which a wave transfers energy
solid, liquid, gas, or combination
Electromagnetic waves are NOT Mechanical waves because they do not need a medium (e.g. visible light, x-rays)
Types of Mechanical Waves:
Longitudinal Waves (aka compression): Like sound, slinky
Transverse Waves: Like water waves, jump ropes, stadium waves
Electromagnetic waves (light, xrays,etc) are transverse but NOT Mechanical waves

5. also known as compression
Longitudinal Wave
also known as compression
wave disturbance moves in direction wave moves (Slinky)
Vibration of the medium is parallel to the direction the wave travels
Rarefaction (area where particles in medium are spread out)
Compression (area where particles in medium are close together)
examples: sound, earthquake

6. Longitudinal Waves
The source of the wave move side to side. Wave transfers energy from left to right. =>The particles in the medium move parallel to the direction that the wave travels.

7. Compressional Longitudinal wave
On a compressional wave the area squeezed together is called the compression. The areas spread out are called the rarefaction.
The wavelength is the distance from the center of one compression to the center of the next compression.

8. Longitudinal Waves: Anatomy
Amount of compression corresponds to amount of energy  AMPLITUDE.
compression
wavelength
rarefaction

9. Sound Wave - Longitudinal
Compression
Amplitude
Rarefaction
WAVELENGTH

10. Wave moves perpendicular to direction of motion (Regular spring)
Transverse wave
Wave moves perpendicular to direction of motion (Regular spring)
Crests (top), troughs (bottom), rest position
nodes and antinodes
example: light

11. Transverse Waves
The source of the wave moves up and down. Wave transfers energy from right to left. =>The particles in the medium move perpendicular to the direction that the wave travels.

12. What are the parts of a wave? Transverse wave
The crest is the highest point on a transverse wave. The trough is the lowest point on a transverse wave.
The rest position of the wave is called the node or nodal line.
The wavelength is the distance from one point on the wave to the next corresponding adjacent point.

13. Transverse Waves: Anatomy
corresponds to the amount of energy carried by the wave
crest
wavelength
crest
amplitude
nodes
troughs

14. Draw & Label these waves…their type and parts
Draw & Label these waves…their type and parts. Also list examples of each!! 1 1 2 2 3 ex 3 5 7 8 4 4 ex 6

16. measured in meters (or km, cm, etc)
Wavelength
Wavelength (λ)- distance between two identical points on consecutive waves
measured in meters (or km, cm, etc)
Increasing the frequency of a wave decreases its wavelength.

17. What is the frequency of a wave? Frequency: # cycles per second
Period vs. Frequency
What is the frequency of a wave?
Frequency: # cycles per second
Period: # seconds per cycle
Unit: seconds (s)
Period = 1/frequency P = 1/f f = 1/P
The higher the frequency, the shorter the period.
Inverse Relationship

18. f = #cycles sec Frequency of a Wave
Frequency: # of cycles per second - measured in Hertz (Hz) or 1/s or s-1
f = #cycles
sec
0 sec
2 sec

20. Frequency of a Wave
What is the frequency?
0 sec
2 sec

21. Wavelength and frequency are inversely related.
The smaller the wavelength, the more times it will pass through a point in one second.
The larger the wavelength, the fewer times it will pass through a point in one second.

22. Types of Mechanical Waves:
Longitudinal Waves (aka compression): Like sound, slinky
Transverse Waves: Like water waves, jump ropes, stadium waves
Electromagnetic waves (light, xrays,etc) are transverse but NOT Mechanical waves

23. Wave Speed
Speed of the wave is determined by the medium.
Temperature affects the speed.
Sound travels fastest through a solid.
Wave speed
Solid liquid gas
Fastest Slowest

24. v =  × f Velocity ( v ) v: velocity (m/s) : wavelength (m)
Measuring Waves
Velocity ( v )
speed of a wave as it moves forward
depends on wave type and medium
measured in m/s (or km/s, cm/s, etc)
v =  × f
v: velocity (m/s)
: wavelength (m)
f: frequency (Hz)

25. f v  GIVEN: WORK: v = ? v =  × f v = (3.2 m)(0.60 Hz)  = 3.2 m
EX: Find the velocity of a wave in a wave pool if its wavelength is 3.2 m and its frequency is 0.60 Hz.
GIVEN:
v = ?
 = 3.2 m
f = 0.60 Hz
WORK:
v =  × f
v = (3.2 m)(0.60 Hz)  v f

26. f v  GIVEN: WORK:  = 417 m f = v ÷  f = (5000 m/s) ÷ (417 m)
EX: An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency?
GIVEN:
 = 417 m
v = 5000 m/s
f = ?
WORK:
f = v ÷ 
f = (5000 m/s) ÷ (417 m)  v f

27. A tuning fork has a frequency of 280 hertz (Hz), and the wavelength of the sound produced is 1.5m. Calculate the velocity of the wave.
A wave is moving toward the shore with a velocity of 5.0 m/s. If its frequency is 2.5Hz what is its wavelength?

28. Distance from crest or trough to rest position in transverse wave.
Amplitude
Amplitude - max displacement from its rest position (also known as wave height)
measured in meters (or km, cm, etc)
Example – dropping a pebble in the water vs. doing a “cannonball” jump into the water
Distance from crest or trough to rest position in transverse wave.
Distance between compressions in longitudinal waves.
VERY IMPORTANT: The more energy a wave has, the greater is its amplitude!!!

29. Reflection—bouncing back of a wave as it hits a reflective surface.
The behavior of waves
Reflection—bouncing back of a wave as it hits a reflective surface.
Refraction—bending of a wave as it moves from one substance to another.
Diffraction—Bending(spreading) of a wave moving through the same substance(around a corner)
Interference—combining of 2 or more waves as they pass “through” each other.

30. All types of waves can be reflected
Reflection
Occurs when a wave strikes an object it cannot pass through and bounces off of it.
All types of waves can be reflected

31. The greater the change in speed, the more the wave bends
Refraction
Bending of a wave caused by a change in its speed as it moves from one medium to another.
The greater the change in speed, the more the wave bends

33. Refraction of Sound

34. An object causes a wave to change direction and bend toward it.
Diffraction
An object causes a wave to change direction and bend toward it.
Occurs when waves pass around an object.
The smaller the opening, the greater the diffraction

35. Interference When two or more waves overlap and combine to form a new wave.
Constructive Interference
Destructive Interference
Waves “add together” because they are in “phase” with one another.
Waves “cancel” because they are out of “phase” with each other.

36. What is the Doppler Effect?
Is the Apparent change in frequency (pitch) that occurs because of the waves either “squishing” together (shorter wavelengths) or spreading apart (longer wavelengths).
The velocity of the sound wave doesn’t change, so if the wavelength changes, the frequency must also.

38. Doppler Effect
If the sound source and the detector (person) are moving toward each other, frequency is higher. If they are moving apart, frequency is lower.

40. What is sonar?
Sonar is a system that uses the reflection of underwater sound waves to detect objects. This has been used to find sunken ships and schools of fish.