1. Chapter 25
Vibrations and Waves

2. Waves transmit energy through space and time.

3. The source of all
waves is something
that vibrates.
A repeating, back-and-forth motion about an equilibrium position is a vibration.

4. Some Definitions A wave is a disturbance that propagates through space
and time, usually with
transference of energy.
Propagate - to move Transference - a transfer
A wave moves energy from one place to another.

5. All waves have Crest - Highest point on the wave
trough
Crest - Highest point on the wave
Trough - lowest point on the wave
Wavelength () lambda.
length from crest to crest
Measured in meters.
Amplitude - height of wave
Measured in meters about the midpoint.

6. Frequency The amount of cycles per second. Measured in Hertz (Hz.)
Ex. A dog wags its tail 5 times a second.
Tail wags with a frequency of 5 Hz.
Math
Wavelength times frequency = wave speed.

7. Try This! Use the math formula from the previous slide.
Sound travels at 340 m/sec.
A good low bass note of c# has a frequency of about 34Hz.
What is the wavelength of the note?

8. Period The time it takes to move through one cycle is the period
The period is the reciprocal of the frequency.
They are inversely
related.
We use the Greek
letter  (tau) to
represent the period.

9.  The Pendulum The time of a back-and-forth swing of the pendulum
is called the period.
The period is measured in seconds.
We use the Greek letter (tau)
to represent the period 

10. More about the Pendulum
The period of the pendulum depends on
the length of a pendulum
and
the acceleration of gravity.

11. Simple harmonic motion
The back-and-forth vibratory motion (often called oscillatory motion) of a swinging pendulum is called simple harmonic motion.
The pendulum is an example of simple harmonic motion.

12. Two Kinds of Waves Fundamentally, there are two types of waves.
Before we get to the two kinds of waves, you need to know a word.
Medium - any solid, liquid, or gas.

13. Transverse Waves
Whenever the amplitude of the wave is at right angles to the direction in which a wave travels, the wave is a transverse wave.
Transverse waves do not need a medium to propagate through.

14. Longitudinal Waves
When the particles oscillate parallel to or along the direction of the wave rather than at right angles to it, the wave is a longitudinal wave.
Sometimes called compression waves.
Longitudinal waves need a medium to propagate through.

15. Difference between Transverse and Longitudinal Waves

16. Standing Waves
When waves hit solid boundaries, like the walls of a room, standing waves can appear.
It appears that the waves is stationary, but it is really moving in a way that makes it look like that.

17. Nodes and Antinodes Node- Place that does not move
Antinode- Place of maximum displacement
Antinodes are half way between nodes
Anti-
Node
Node
Node
Anti-
Node
Anti-
Node

18. Interference When two waves cross paths, they are said to interfere.
This interference can be broken up into two categories.

19. Constructive or Destructive
Constructive Interference- When two or more waves interfere and the resultant wave has a larger amplitude.
Destructive Interference- When two or more waves interfere and the resultant wave has a smaller amplitude than the original waves.

21. Doppler Effect
The shift in frequency due to the motion of the source of waves.
As a wave source approaches, an observer encounters waves with a higher frequency. As the wave source moves away, an observer encounters waves with a lower frequency.

22. Bow Waves
A bow wave occurs when a wave source moves faster than the waves it produces.

23. Shock Waves

24. Slinky Lab Wrap Up
Describe the amplitude of the first waves that you made. What are these waves called?
Describe the amplitude of the second kind of waves that you made. What are these waves called?
How are the amplitudes of the two waves different in relation to the way the waves propagate?
What happened to the waves as you made the slinky tighter?

25. Summary of Tick Tock Lab
Answer the following questions
Define Period
Why does the mass of the pendulum fall towards the ground?
What are the two things that change the period of the pendulum?
What was the length of the pendulum with a period of 1 sec.?

26. Mini Quiz Get out a piece of paper.
Define Transverse wave
Define Longitudinal Wave
Are sound waves different than light waves?