Matter and Energy - Waves

Introducing Waves

Waves are caused by disturbances in a medium that transfer energy without a net transfer of matter.

Waves transfer energy from one place to another, but they don’t transfer any matter.

How do they transfer energy

To travel from one place to another the waves vibrate (oscillate.)

• The distance is how far the wave has travelled from its starting point

• The displacement is how far from the equilibrium point the wave has oscillated

Transverse Waves

As energy passes (propagates) through a medium, the particles vibrate/oscillate perpendicular/at right angles (90°) to the energy transfer.

In the animation below, the energy moves towards the right, but the slinky is only moving up and down.

Longitudinal waves

As energy propagates through a medium, the particles vibrate back-and-forth in the same direction as the energy transfer.

In the animation below, the energy moves towards the right and the slinky moves left and right. (watch the piece of sticky tape above the e in disturbance)

Compression

A region of higher-than-normal pressure. (molecules squished together)

Rarefaction

A region of lower-than-normal air pressure. (molecules spread out)

Sound Waves

A sound wave, also known as an acoustic wave, is a type of mechanical wave that propagates through a medium, (air, water, or solids) due to the vibration of an object.

Wave Propagation

The movement of the wave through a medium.

Propagates/propagation - movement of the wave.

Wave Speed ( 𝑣)

How fast the wave is moving.

Wavelength (λ)

Distance between two compressions (crests on graph).

Units: metres, m.

Amplitude

Maximum increase/decrease in vertical scale from median.

Units depends on vert axis variable.

Large amplitude = loud volume Small amplitude = quiet volume

Pressure in Sound Waves

- Peaks show high pressure

- Median shows normal air pressure

- Troughs show low pressure.

Frequency (f)

Number of oscillations or waves per second being produced.

Units: Hertz, Hz.

Period (T)

The amount of time it takes for a wave to complete one cycle, or wavelength. Units: seconds, s.