1. waves

2. definition
A wave is a wiggle in space and time.
A wave is an oscillation (a repeated
disturbance).

3. what does the waving?
1. mechanical waves
the wave disturbance occurs in a medium
(substance)
e.g., pressure disturbance in air (sound waves)
disturbance of water surface (water waves)
2. electromagnetic waves
require no medium
e.g., light, x-rays

4. what direction is the waving done in?
There are two directions associated
with waves.
1. propagation direction
Where the wave goes.
Where the energy goes.

5. 2. oscillation direction
The direction in which individual
particles (or fields) move.

6. If propagation and oscillation are at right
angles, it’s a transverse wave.
propagation
oscillation

7. wave on a string (PHeT)
crowd doing the wave (video)

9. There were once water ripples on Mars.

11. Some bats can
detect the ripples
made by frogs when
calling for mates.
The ripples are like a
target, with a juicy
meal at the center!

12. Anatomy of a transverse wave
wavelength

13. Anatomy of a transverse wave
amplitude
amplitude = vertical distance from
center line to wave peak. Units: m

14. If propagation and oscillation are in the
same direction, it’s a longitudinal wave.
oscillation
propagation

15. ancient video on sound
slinky

16. Anatomy of a longitudinal wave
high pressure
low pressure
compression = region of high pressure
rarefaction = region of low pressure

17. Anatomy of a longitudinal wave
compression
wavelength
rarefaction

18. pressure
amplitude = maximum pressure –
average pressure.
average
amplitude

19. the wave equation
frequency = number of waves
passing a fixed point each second.
Symbol: f
Units: Hz (“Hertz”)

20. the wave equation
Let’s count the number of waves
passing in 1 sec:
t=0s
t=1s
2.25 waves

21. the wave equation
frequency = number of waves
passing a fixed point each second.
f = 2.25 Hz in the example from the
previous slide.

22. the wave equation
t=1s

23. the wave equation
t=1s

24. the wave equation

25. the wave equation
the wave equation

26. the wave equation