1. 1 - Waves
…Review from Overview

2. Throw it in, and what do you see?
You are standing on a dock at your favorite lake. You have a rock in your hand, what do you do with it?
Throw it in, and what do you see?

3. Waves
Waves are not just what happens in water or a way to say good bye to someone
Waves are all around us. Most of the things that we do everyday involve waves but you may not realize it, yet! About all of you have something with you today that relies on waves to operate correctly. When we talk about waves though, we need to specify what type of wave we are talking about. There are two types of waves and we will discuss the differences between the two.
Foucault Pendulum

4. Types of Waves Longitudinal Waves
Particles vibrate in the same direction the wave travels
Ex. Sound

5. Types of Waves Transverse Waves-
Particles vibrate perpendicular (up and down) when the wave moves left or right
Ex. Waves on a rope, light waves

6. Parts of a Wave Crest- highest point Trough- lowest point
Amplitude- maximum height from middle to crest or trough
crest
amplitude
trough

7. Parts of a Wave
Wavelength- distance between two consecutive crests or troughs
Wavelength

8. Parts of a Wave Period- time taken for one complete cycle
Yesterday we talked about period having the units of seconds, why was that?

9. Frequency - how often something happens - number of cycles / unit time
- Hertz = cycles / second
How many waves pass the white line? 2
If that took 1 second, what is the frequency of the wave?
frequency = cycles / second
= 2 / 1 s
= 2 Hz
If you have a lot of headaches, a doctor might say, “ How frequency are your headaches?” and you might say, “ once a week.”

10. How many waves pass the white line?6
If that took 3 second, what is the frequency of the wave?
frequency = cycles / second
= 6 / 3 s
= 2 Hz

11. Example Problems
1) Billy takes his pulse and counts 22 heartbeats in 30 seconds, what is the frequency in hertz?
frequency = cycles / second
= 22 / 30 s
= 0.73 Hz
2) Ian takes his pulse and counts 54 heartbeats in 1 minute. What is the frequency in hertz?
= 54 / 60 s
= 0.90 Hz

12. period (s) frequency (Hz)

13. More Example Problems
3) If something has a frequency of 4 Hz, what is its period?
T=1 / f
T=1 / 4 Hz
T= 0.25 s
4) If something has a period of 3 seconds, what is its frequency?
f =1 / T
f =1 / 3 s
f = 0.3 Hz
5) At an amusement park, a giant ship swings back and forth with a frequency of Hz. How long does it take the ship to swing back and forth once?
T=1 / Hz
T=8 s

14. Wave Speed - distance per unit time
Speed (m/s) distance (m)
time (s)
Speed (m/s) frequency (1/s)
wavelength (m)

15. More Example Problems v=fλ v= 2 Hz · 0.4 m v= 0.8 m/s
6) Calculate the speed of ocean waves that are 0.4 m apart and have a frequency of 2 Hz.
v=fλ
v= 2 Hz · 0.4 m
v= 0.8 m/s
7) If a wave traveling at the speed of light (3x108 m/s) has a frequency of 95.5 MHz, what is the wavelength? (1 megahertz = 1x106 hertz )
f=95.5 MHz = 9.55x107 Hz
v = f λ
3x108 m/s = 9.55x107 Hz · λ
λ = 3.14 m

16. Interferences
Constructive interferences - Crests overlap crests increasing the amplitude

17. Interferences
Destructive Interferences - Crests overlap troughs decreasing the amplitude

18. …so in lab the #1 rule in safety is’ “THINK before you ACT!”
Physics Lab Safety
Think before you act.
…so in lab the #1 rule in safety is’ “THINK before you ACT!”