1. Physics 20 Mechanical Waves
Universal Wave Equation

2. Waves So far we have been studying pulses
Pulses are really only half a wave. They are helpful to introduce waves, but fail to give the full effect
“l” is used to indicate the length of a pulse
The Greek letter Lambda is used to denote a wavelength
In water, a crest is the pos. displacement from the equilibrium while a trough is the neg. displacement.
In other waves a crest and trough are used to denote the two regions on the wave that are on opposite sides of the equilibrium.

3. Other variables
Frequency (f), period (T), and amplitude (a) denote the same thing in waves as they do in SHM
The period for a wave is twice the period of a pulse, which should make sense.
Then it must also make sense that lambda for a wave is twice the length of a pulse.

4. Universal Wave Equation
Recall that the length of a pulse (l) = vt
Well the length of a wavelength (lambda) = vT
T = 1/f
Solving for v we get?

5. Let’s take a look at this formula …
The speed of the wave depends on …
Let’s say we want to find out why a wave slows down when it hits shallow water.
We know the frequency of the waves is the same in deep or shallow water
We know that the speed decreased
What could this be attributed to?
Let’s Equate the Universal wave equation for the two waves since we know that frequencies are equal and see what happens.

7. Example 8.2 Page 409
To generate waves in a stretched spring, you oscillate your hand back and forth at a frequency of 2.00 Hz. If the speed of the waves in the spring is 5.40 m/s, what is the wavelength?

8. Assignment Reading: Questions: Pearson Physics pages 408 – 410