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WAVES

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WAVES

- sometimes called oscillatory motion

- the back and forth vibratory motion of a swinging pendulum
- sine curve - the shape of the line a swinging pendulum makes over a constantly moving surface

A wave is a disturbance that carries energy through matter or space.

Medium - the matter that a wave travels through. Examples: water, air, steel, the Earth

Mechanical Waves - waves that require a medium.

All waves, except light, are mechanical waves.

Electromagnetic Waves - waves that consist of changing electric and magnetic fields in space.

Crests - the high points of a wave

Troughs - the low points of a wave

Amplitude - the distance from the midpoint to the crest (or trough) of a wave

Wavelength - the distance between successive identical parts of a wave (crest to crest or trough to trough)

Period - the time it takes for one complete wave

- time ÷ # of waves

- measured in time units

Frequency - the number of waves that pass a point in a given amount of time

- # of waves ÷ time (usually seconds)

- measured in Hertz (Hz)

Period = 1

frequency

Frequency = 1

period

- What is the frequency, in hertz, that corresponds to each of the following periods?
a. 0.10 s

b. 5 s

c. 1/60 s

d. 24 h

2. What is the period, in seconds, that corresponds to each of the following frequencies?

a. 10 Hz

b. 0.2 Hz

c. 60 Hz

d. 0.8 Hz

3. A metronome is set so that it makes ten complete vibrations in 12 seconds. Find the frequency of the metronome.

In linear motion:

speed = distance(m/s)

time

In wave motion:

speed = wavelength x frequency

v = ƒ(m · 1/s = m/s)

A wave with wavelength 10 m passes a pier with a frequency of 2 Hz. What is the speed of the wave?

A wave with wavelength 10 m passes a pier with a frequency of 2 Hz. What is the speed of the wave?

- = 10 m
- = 2 Hz
v = ?

A wave with wavelength 10 m passes a pier with a frequency of 2 Hz. What is the speed of the wave?

- = 10 mv =
- = 2 Hzv = (10m)(2Hz)
v = ?v = 20 m/s

If a water wave vibrates up and down two times each second and the distance between wave crests is 1.5 m, what is the frequency of the wave?

What is its wavelength?

What is its speed?

If a water wave vibrates up and down two times each second and the distance between wave crests is 1.5 m, what is the frequency of the wave?

= 2 Hz

What is its wavelength?

= 1.5 m

What is its speed?v = 3 m/s

While sitting on a pier, Carlos notices that incoming waves are 2.0 m between crests. If the waves lap against the pier every 0.5 s, find

- the frequency.
b) the speed of the wave.

While sitting on a pier, Carlos notices that incoming waves are 2.0 m between crests. If the waves lap against the pier every 0.5 s, find

- the frequency.
= 2 Hz

b) the speed of the wave.

v = 4 m/s

Transverse Waves - the motion of the medium is at right angles to the direction in which the wave travels.

(Look like a sine curve.)

Example: water waves, light waves

Longitudinal Waves - the particles move along the direction of the wave (rather than at right angles to it).

Example: sound waves

Standing waves occur when the original wave and the reflected wave combine to form a wave where parts of the medium do not move.