1. Waves
Chapter 11 Section 1

2. What is a wave?
A wave is a repeating disturbance or movement that transfers energy through matter or space
Waves transfer energy NOT matter
Medium: the matter through which a wave travels; i.e. water, air

3. Motion of a Duck on a Wave

4. Water Wave

5. Mechanical Waves Waves that can travel only through matter
There are two types:
Transverse waves (water, and some seismic waves)
Longitudinal waves (sound, spring)
Requires a medium!!!!!!!

6. Longitudinal (compressional) Waves
Particles in the medium move parallel to the direction of the waves.
  particle motion  
  wave motion  
The dense areas are called compressions.
The less dense areas are rarefactions.

7. Transverse Waves
Particles in the medium move perpendicular to the direction of the waves.
wave motion
particlemotion

8. Parts of a Wave Crest: the highest point (top) of a transverse wave.
Trough: the lowest point (bottom) of a transverse wave.
Wavelength: the distance from any point on a wave to the same point on the next wave. (ex: crest to crest)
Amplitude: the height measured from the resting position.

9. Parts of a Wave
crest
wavelength
amplitude
trough

10. Seismic Waves
Seismic waves are a combination of compressional and transverse waves
1. They can travel along the earth’s surface
2. When objects on the Earth’s surface absorb some of the energy carried by seismic waves, they move and shake
Compressional
Transverse

11. Greater amplitude = more energy.
Measures the amount of
energy in a wave.
Greater amplitude = more energy.

12. FREQUENCY
The rate at which waves pass (the # of full wavelengths that pass a point in one second).
Symbol: f
Unit: Hertz (Hz)
1 Hertz = 1 vibration per second
Frequency is 1 / T

13. WAVE SPEED How fast a wave moves. Symbol: v Unit: m/s
Wave speed is determined by the medium. Generally, waves pass through solids faster b/c particles are closer and can pass vibrations to each other more quickly.

14. EQUATIONS v = f · λ f = v / λ λ = v / f v UNITS: λ = meters (m)
Wave speed = frequency times wavelength
v = f · λ f = v / λ
λ = v / f
UNITS: λ = meters (m)
f = Hertz (Hz)
v = m/s v
f λ

15. The string of a piano that produces the note middle C vibrates with a frequency of 264 Hz. If the sound waves produces have a wavelength of 1.30 m in air, what is the speed of sound in air?
f = 264 Hz
λ = 1.30 m
v = ?
v = 264 Hz (1.30 m)
v = f · λ
v = m/s

16. A water wave has a speed of 1. 3 m/s
A water wave has a speed of 1.3 m/s. A person sitting on a pier observes that it takes 1.2 s for a full wavelength to pass the edge of the pier. What is the wavelength of the water wave?
v = 1.3 m/s
T = 1.2 s
f = 1 / T = 1 / 1.2 s
= 0.83 Hz
λ = ?
λ = 1.3 m/s / 0.83 Hz
λ = v / f
λ = 1.57 m