INTRODUCTION TO WAVES

WAVES

• Waves are a disturbance that travels through space or matter

• Waves transmit energy

TYPES OF WAVES• There are 2 types of waves

1. Longitudinal Waves• A longitudinal wave is when the displacement is in the same

direction (parallel to) that the energy is travelling• Example – Think of a Slinky. If you stretch out a slinky and push in one

side, it will bunch up in one area. That bunched up area will travel forward through the slinky. This is an example of a longitudinal Wave

• These are sometimes called pressure waves or compression waves

TYPES OF WAVES• Longitudinal Waves• Longitudinal waves are mechanical waves• Mechanical waves transmit energy through a medium, such

as matter

• In a longitudinal wave, there are 2 main areas that we see• Compression – where all of the particles are bunches

together• Rarefaction – where the particles are spread far apart

• Examples of longitudinal waves are sound waves or p-waves during an earthquake

TYPES OF WAVES• Sound waves act as longitudinal waves• Sound waves are created when force is exerted on air• The air bunches together where it was pushed• The air that was pushed runs into other air particles and

transmits its energy• This moves the wave forward, transmitting energy

Compression

Rarefaction

TYPES OF WAVES• Earthquakes and longitudinal waves• Earthquakes are felt after the tectonic plates of the Earth shift• This transmits energy through the Earth itself• We feel this as an earthquake• The P-Wave is a longitudinal wave and is the first wave felt in an

earthquake

TYPES OF WAVES2. Transverse Waves• A transverse wave is when the displacement is perpendicular to the direction the energy is travelling.• Example – Think of a rope. If you move the end of the rope up

and down, the rope will form a wave pattern and the energy will travel down the rope.

TYPES OF WAVES

• Transverse Waves• Transverse waves can be mechanical waves• This means then can travel through matter

• Transverse waves can also be electromagnetic waves• These are waves that can travel through a vacuum or space• They do not need matter to continue moving.

• We usually call electromagnetic waves light

TYPES OF WAVES

• Earthquakes also produce transverse waves• The second wave to hit in an earthquake is the s-wave• It is a transverse wave• It moves the ground side-to-side shaking the earth

back and forth

TYPES OF WAVES• Although longitudinal and transverse waves may look different,

mathematically they are still the same

• A longitudinal wave can be plotted as areas of high particle density vs. time to make a repeating pattern

• A transverse wave, when plotted, shows the same pattern over time

THE MATHEMATICS OF PERIODIC WAVES

• To understand how periodic waves work, we must be able to identify the parts of a periodic wave• Crest – The peak, or top, of the wave• Trough – the bottom of the wave

THE MATHEMATICS OF WAVES

• Amplitude – the height (or low) that a wave reaches from the resting point• This is NOT the maximum movement of the wave up and

down

• Essentially it is how high or how low a wave goes from the middle

THE MATHEMATICS OF WAVES• Period – The period is the time that it takes for a wave to

complete one cycle• Basically how long it takes (in seconds) for a wave to

go from peak-to-peak or trough-to-trough

• A wave’s period is measured in seconds/cycle (s/cycle)• Period gets the symbol T.

THE MATHEMATICS OF WAVES• Frequency – the frequency of a wave is the inverse of the period

(1/T)• It is the number of cycles that wave can complete in 1 second

• If you could only see one portion of a wave and watched it for one second, the number of times the string moved up, down, and up again would be the frequency.

• Frequency is measure in the units cyles/second• Cycles/second is also called Hertz (Hz)• Frequency gets the symbol f

THE MATHEMATICS OF WAVES• Wavelength – the distance it takes for a wave to complete one

cycle• Basically, how far a wave travels to go from peak-to-peak or

trough-to-trough• Wavelength is a distance and is measured in metres/cycle• We usually don’t worry about saying cycle because we know

it is a wave and it is completing cycles• Wavelength gets the symbol lambda (λ)

THINGS YOU SHOULD KNOW

• Wave

• Longitudinal Wave• Mechanical Wave

• Transverse Wave• Electromagnetic Waves

• Crests

• Troughs

• Amplitude

• Period

• Frequency

• Wavelength