1. JQ: Draw a transverse and a longitudinal wave
JQ: Draw a transverse and a longitudinal wave. Where are each found in nature?
Agenda
Relationships among speed, wavelength, and frequency.

2. Transverse Waves
The differences between the two can be seen

3. Wave Frequency
Frequency measures how often something happens over a certain amount of time.
We can measure how many times a pulse passes a fixed point over a given amount of time, and this will give us the frequency.

4. Wave Frequency
Suppose I wiggle a slinky back and forth, and count that 6 waves pass a point in 2 seconds. What would the frequency be?
3 cycles / second
3 Hz
we use the term Hertz (Hz) to stand for cycles per second.

5. Wave Period
The period describes the time it takes for one cycle to complete.
A pendulum is a simple way to see this.
It also is the reciprocal of the frequency.
T = 1 / f
f = 1 / T

6. Wave Speed
We can use what we know to determine how fast a wave is moving.
What is the formula for velocity?
velocity = distance / time
What distance do we know about a wave
wavelength
and what time do we know
period

7. Wave Speed so if we plug these in we get velocity = length of pulse /
time for pulse to move pass a fixed point
v =  / T
we will use the symbol  to represent wavelength

8. Wave Speed v =  / T but what does T equal so we can also write
T = 1 / f
so we can also write
v = f 
velocity = frequency * wavelength
This is known as the wave equation.
Stop here to do Part C

9. Jerome and Claire are doing the Period of a Pendulum Lab
Jerome and Claire are doing the Period of a Pendulum Lab. They observe that a pendulum makes exactly 10 complete back and forth cycles of motion in 21.8 seconds. Determine the period of the pendulum.
21.8 s / 10 cycles
T = 2.18 s

10. Strong winds can apply a significant enough force to tall skyscrapers to set them into a back-and-forth motion. The amplitudes of these motions are greater at the higher floors and barely observable for the lower floors. It is said that one can even observe the vibrational motion of the Sears Tower in Chicago on a windy day. As the Sears Tower vibrates back and forth, it makes about 8.6 vibrations in 60 seconds. Determine the frequency and the period of vibration of the Sears Tower.

11. It makes about 8. 6 vibrations in 60 seconds
It makes about 8.6 vibrations in 60 seconds. Determine the frequency and the period of vibration of the Sears Tower.
60 s / 8.6 cycles
T = 7s
f = 1/T = 1/7
f = .14 Hz

12. The spin rate of a CD-ROM varies according to the location on the disc from where data is being accessed. When accessing data from the inner circles of the disc, the CD can spin at a rate as high as 400 revolutions per minute. Determine the frequency (in Hertz) and the period (in seconds) of the spinning CD.
f = 400/min = 6.67/s = 6.67 Hz
T = 1/f = 1/6.67 = 15 s

13. v = d/t = 50 m / 21.8 s = 2.29 m/s f = v /  = 2.29 m/s / 9.28 m
A marine weather station detects waves which are 9.28 meters long and 1.65 meters high and travel a distance of 50.0 meters in 21.8 seconds. Determine the speed and the frequency of these waves.
v = d/t
= 50 m / 21.8 s = 2.29 m/s
f = v / 
= 2.29 m/s / 9.28 m
= .247 Hz

14. A wave is traveling in a rope
A wave is traveling in a rope. The diagram below represents a snapshot of the rope at a particular instant in time.
Determine the number of wavelengths which is equal to the horizontal distance between points
a. … C and E on the rope.
b. … C and K on the rope.
c. … A and J on the rope.
d. … B and F on the rope.
e. … D and H on the rope.
f. … E and I on the rope.

15. Answers
a. 1.0 wavelengths b. 3.5 wavelengths c. 4.0 wavelengths d. 1.5 wavelengths e. 2.0 wavelengths f wavelengths