Waves and SoundHonors Physics

Simple Harmonic Motion

Refers to repetitive, cyclical motion (like a pendulum or waves)

Can be described with sine curve

For a pendulum only

g

LT 2

Example problem

The world’s longest Foucault pendulum is in Seattle and it is 21.3 meters long.

What is the period of this pendulum?

What is the frequency of this pendulum?

Period and Frequency

Period (T)

the time for one full cycle

measured in seconds

Frequency (f)

the number of cycles in one second

measured in Hertz (Hz)T

f

fT

1

1

Example problem

A pendulum swings back and forth 12 times in 4.0 seconds.

What is the period of the pendulum?

What is the frequency of the pendulum?

Waves

A wave is a disturbance or oscillation back and forth that transfers energy (but not particles) through space.

Mechanical vs. Electromagnetic

Mechanical Waves

waves that travel through (and require) a physical medium (like water and slinky and sound waves)

Electromagnetic Waves

electric and magnetic disturbances that do NOT require a medium (like light and radio waves)

Waves

Electromagnetic waves

Electromagnetic field disturbances that do NOT require a medium to travel

Ex. Light, radio wave, microwave

Mechanical waves

Wave that requires a physical medium to travel

Ex. Slinky, water, sound

Transverse Longitudinal Transverse

Transverse waves

• Disturbance is perpendicular to the direction of travel (propagation)

• Disturbance is “up and down” and travels “left and right”

Longitudinal waves(compression waves)

• Disturbance is parallel to the direction of travel (propagation)

• Disturbance is right or left and waves travel right or left

Parts of a wave

Wave Velocity

The speed of the wave is determined by the medium only

Frequency and amplitude do not change the speed of a wave

Frequency ( f ) and wavelength ( ) are inversely related

𝑣 =𝑑

𝑡

𝑣 = 𝑓

Example

In the water, you see 7 waves go by in 12 seconds. The distance between crests is 2.5 m. The distance from flat water up to a crest is 1.5 m.

Period = ?

Frequency = ?

Speed of wave = ?

Example

A transverse wave passes through a uniform material medium from left to right, as shown in the diagram below

Which diagram best represents the direction of vibration of the particle, P, of the medium?

What is the wavelength of the transverse wave pictured here?

a) 0.20 m

b) 0.40 m

c) 1.0 m

d) 2.0 m

e) 4.0 m

How many wavelengths are pictured in the diagram?

a) 1.0

b) 2.0

c) 2.5

d) 3.0

e) 5.0

What is the amplitude of the wave pictured in the diagram?

a) 0.20 m

b) 0.40 m

c) 1.0 m

d) 2.0 m

e) 4.0 m

Which points mark the crests of the wave?

List the letter(s) that are in phase with point C?

Interference (Principle of Superposition)• When waves meet at a point in

space, the resulting waveform is the addition of the amplitudes

• Constructive interference amplitudes add together to make bigger wave

• Destructive interference amplitudes subtract and form smaller wave…or cancel for a moment

• Important: waves pass through each other after they interfere (waves are energy)

Example

Two pulses traveling in the same uniform medium approach each other, as shown in the diagram below.

Which diagram best represents the superposition of the two pulses?

Example

Two pulses traveling in the same uniform medium approach each other, as shown in the diagram below.

Which diagram best represents the superposition of the two pulses?

Example

Two pulses traveling in the same uniform medium approach each other, as shown in the diagram below.

Describe what happens after the two waves meet in space.

The two waves will destructively interfere when they meet, but then the two waves will pass through each other and return to their same size and continue moving in the same direction.

Example

The diagram below shows two pulses traveling toward each other in a uniform medium.

Which diagram best represents the medium when the pulses meet at point X?