Waves

Transferring Energy

Waves: traveling disturbance that carries energy from one place to

another

Waves travel through water, but they do not carry the water (or the duck) with them.

What causes waves?

• Vibration: repeated motion starting waves; how waves get their energy

Medium

• Material through which waves travel

Mechanical Waves

• Must have a medium to travel– Examples: ocean waves, sound waves

• Bell jar example

Electromagnetic waves

• Need no medium to travel– Heat waves (radiation)

– Light waves

Transverse waves: move the medium at right angles to the

direction in which the waves travel

vibrationDirection of travel

Longitudinal: waves move the medium parallel to the

direction in which the waves travel.

Sound Waves

Direction of wave travel

Sound waves are longitudinal waves

Wavelength

• The distance between a given point on a wave to the same point on the next wave.

• Most commonly measured from the center of one crest to the center of the next crest.

wavelengthcrest

trough

normal

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Amplitude

• Measured from the crest to the wave normal (wave “at rest”).

• Amplitude is the “power” of the wave

wavelengthcrest

trough

normal

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Frequency

• The number of waves that pass a certain point in one second.

• Besides cycles per second, many times frequency is measured in Hertz (Hz). One Hertz is equal to one cycle per second

Which wave has the longer

wavelength?

Which wave has the higher

frequency?

Which wave has the longer

wavelength?

Which wave has the higher

frequency?

•Wavelength and frequency have an inverse relationship.

•As wavelength increases, frequency decreases.

•Brainpop on Waves

Speed of Waves

Velocity = frequency x wavelength

v = f λ• v = velocity

• f = frequency

• λ = wavelength

Speed of waves practice

• A middle C note has a wavelength of 1.34 meters. Its frequency is 256 Hz. What is the speed of this sound?

• Formula:

• Substitutions:

• Answer:

• The approximate outdoor temperature can be calculated by the number of times a cricket chirps per minute. Sound travels at the same speed (343 m/s) at sea level under the same atmospheric conditions (humidity, temperature, etc.). If a cricket’s chirp has a frequency of 180 Hertz, what is the wavelength of the sound?

• Formula: velocity = frequency x wavelength

• Substitutions:

• Answer: