Topic 5-1

Vibrations

And

Waves

Pendulum Motion

Any motion caused by an object swinging back and forth from a fixed object

Period:The time it takes the object to swing back and forth

Period continued:Only depends on the length of the pendulum and gravity

Simple harmonic motion:Is defined as the back and forth motion of a pendulum, also known as a sine curve

Parts of a wave

Crest:Highest Point

Trough:Lowest point

Amplitude:Length a wave rises or falls from the midpoint

Wavelength:Distance between corresponding points of a wave (λ)

Frequency:How often a wave passes a fixed point per second (f)

Parts of a Wave Continued

Wavelength:Is measured in meters (m)

Frequency:Is measured in hertz (Hz)

Motion:Is caused by a vibration/disturbance in a given medium

Types of Waves

Transverse:

Is a “traditional” wave caused by a back and forth motion

Longitudinal:

Waves where compressions cause vibrations

Both waves act the same way; they are just formed differently

Wave Velocity

Will depend on the medium it is passing through

Example:

Sound travels at roughly 340 m/s through the air and roughly 4 times faster through water

Equals:

v = λ f

Velocity=wavelength times frequency

Special Waves:

Radio waves and light waves travel with a velocity = 3x108 m/s

Sample Questions

Radio station WKLB in Boston broadcasts at a frequency of 99.5 MHz. What is the wavelength of the radio wave emitted?

Clay is surfing on a wave that propels him toward the beach with a speed of 5 m/s. The crests are 20 m apart. What is the waves frequency?

Wave Interference

Is caused when waves begin to overlap and cause patterns

Constructive Interference:

Increases in amplitude - “In phase”

Destructive Interference:

Crest of one wave fills in the trough of another wave - “Out of Phase”

Wave Interference Continued

- Grey “spokes” represent destructive interference

- Black and white areas represent constructive interference

Standing Wave

Node:

No amplitude

Anti-node:

Area of highest amplitude (1/2 way between nodes)

(the higher the amplitude, the more energy in the wave)

Doppler Effect (sound)Approaching effect:

Pitch is perceived to be higher because the source is getting closer & frequency increases

Departing effect:

Pitch is perceived to be lower because waves have a chance to separate & frequency decreases

Reflection

• When a wave strikes a barrier and bounces back

Refraction

• The bending of waves in different mediums or different depths of water

Resonance

Literally means resound.

It is an increase in sound waves.

Can cause other objects to vibrate

Diffraction

• The bending and spreading of a wave when passing through an opening

Diffraction Gratings

• Used to separate light at different wavelengths– Longer wavelength light, slits closer together causes

larger interference pattern– Shorter wavelength light, slits further apart causes

smaller interference pattern

Applications

Radar Gun (police or baseball radar gun)

They read waves bouncing back from a moving object.

This is how a moving DPS Officer can get you for speeding.

Perceived frequency is equal to actual frequency times speed of sound plus the observers speed divided by the speed of sound minus the sources speed.

Mathematically:

fp = fa [(v+vo)/(v-vs)]

Sample Questions

Sitting on the beach at Coney Island one afternoon, Sunny finds herself under the flight path of Kennedy Airport. What frequency will sunny hear as the jet, whose engine emits a 1000Hz sound and flies towards her at a speed of 100 m/s?

What is the frequency of the same jet as it flies away from Sunny?