Waves (Years 8–11) — Science

Drop a pebble into a still pond and rings spread out across the surface. A leaf floating nearby bobs up and down but doesn't sail off toward the edge. That is the secret of every wave: it carries energy from one place to another without carrying the stuff it travels through along with it.

Why this matters: Light, sound, radio, X-rays, the ripples in a slinky and the tremors of an earthquake are all waves. Learn the handful of words and one equation on this page and you can describe every single one of them.

Amplitude = height from the middle; wavelength = one full wave

Two ways a wave can wobble

Waves come in exactly two flavours, and the difference is simply the direction the wobble points compared with the direction the wave travels.

Transverse — the vibration is at right angles (90 degrees) to the travel direction. Picture a skipping rope: you flick your hand up and down, but the wave races along the rope. Light and water waves are transverse.
Longitudinal — the vibration is along the same line the wave travels. Picture a slinky you push and pull: squashed regions (compressions) and stretched regions chase each other down the coils. Sound is longitudinal.

A longitudinal wave: coils bunch into compressions then spread apart, along the travel direction.

The words that describe any wave

Three measurements let you pin down any wave exactly:

Amplitude — the height of the wave measured from the middle (rest) line to a peak. Bigger amplitude means more energy: a loud sound or a bright light.
Wavelength (λ) — the length of one complete wave, e.g. peak to the next peak. Measured in metres (m).
Frequency (f) — how many complete waves pass a point each second. Measured in hertz (Hz). One hertz is one wave per second.

Frequency counts waves passing each second. More waves squeezed in = higher frequency.

Feature	Transverse	Longitudinal
Wobble direction	Across travel	Along travel
Example	Light, water	Sound
Can pass through empty space?	✓ (light can)	✗ (sound cannot)

The one equation to know

Wave speed = frequency × wavelength, written v = f λ. The speed comes out in metres per second (m/s) when frequency is in Hz and wavelength is in m. It makes sense: if lots of waves pass each second (high f) and each is long (big λ), the wave must be racing along.

Worked reasoning. A wave has a frequency of 5 Hz and a wavelength of 2 m. First ask: "which equation links these?" — v = f λ. Now substitute: v = 5 × 2 = 10 m/s. Always check the units line up: hertz times metres gives metres per second, exactly what a speed should be.

v = f λ: multiply frequency by wavelength to get wave speed.

Common mix-up: confusing amplitude with wavelength. Amplitude is the height (up from the middle) and tells you how much energy the wave carries; wavelength is the length (along the wave) of one full cycle. One goes up, the other goes along.

Memory hook: Transverse waves wobble aT right angles; longitudinal waves line up along. And for the sum, "v equals f lambda" — fast fingers love metres.