6.1-6.3Vibrations and Waves

J. PulickeelSPH3U1

January 2010

What is a Wave?A wave is a disturbance that transfers energy through matter or space.

a wave is the motion of a disturbance

What is a Wave?Does a wave need matter to be a wave? No it does not. Electromagnetic waves (Light, heat, x rays, radio waves ) can travel through the vacuum of space.

Recall...Wavelength λ (m)

Approximate Wavelength Scale

Frequency (Hz)

Visible Light Spectrum

400 nm 700 nm

What is a Wave?Other waves travel through a medium like rope, water, sand, air, people (at a baseball game), etc... These are called Mechanical Waves.

We will be talking about mechanical waves in this unit.

What makes a waveA wave that consists of a single pulse is

called a pulse wave.

This can be done with a single flick of your wrist.

Click here for Phet Animation

What makes a waveWhenever the source of a wave’s motion is a

periodic motion, such as the motion of your hand moving up and down repeatedly, a periodic wave is produced.

Notice that the individual particle of the wave does not change location. Its displacement is 0.

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Transverse wavesA second type of wave is a

transverse wave.In a transverse wave the pulse

travels perpendicular to the disturbance or the rest axis.

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Transverse WavesTransverse waves occur when we wiggle the

slinky back and forth or when the source disturbance follows a periodic motion.

The wave formed here is a SINE wave.

Transverse vs. Longtitudal Wave Animation

Parts of a Transverse Wave

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Longitudinal Wave

The wave we see here is a longitudinal wave.

The medium particles vibrate parallel to the motion of the pulse.

This is the same type of wave that we use to transfer sound.

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Longitudinal Wave

rarefaction

compression

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Transverse vs. Longitudinal Waves

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Transverse vs. Longitudinal Waves

Water WavesWater waves are a combination of both

longitudinal and transverse motions. As a wave travels through the waver, the

particles travel in clockwise circles. The radius of the circles decreases as the depth into the water increases.

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Anatomy of a WaveConsider the below wave. Label the

wavelength, crest, trough and amplitude.How many cycles are illustrated?

What points (E,G,J) are in phase with B ?

Which points (E,G,J) are out of phase with B?

Wave RacesThe waves have different but

similar

Which wave would with the wave race (have one oscillation pass the blue line first)?

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Wave Period (T) seconds/cycle

It is the time it takes for one cycle to complete.

86 400 seconds/cycle moon around earth31  556 926 seconds/cycle earth around the

sun

It also is the reciprocal of the frequency.

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Wave Frequency (f) # of cycles/secondThe frequency measure how often something happens

over a certain amount of time.

We can measure how many times a pulse passes a fixed point over a given amount of time, and this will give us the frequency.

The frequency is exactly the same as the source. It never changes, even if its speed and wavelength do!

A slinky back and forth, and 6 waves pass a point in 2 seconds. What would the frequency be?

3 cycles / second3 Hz

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Wave Speed m/sT = s/cycle f = # of cycles/s λ= m

v = f λ