The Wave Machine
From ripples to sound to light: tell transverse from longitudinal waves, label a wave's parts, and link speed, frequency and wavelength with v = f λ.
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The Wave Machine 🌊
Ripples on a pond, sound in the air, light from the Sun — all are **waves**. A wave is a **vibration** that travels, carrying energy along with it. Learn a handful of terms and one equation and you can describe any of them.
Waves carry energy, not matter ⚡
A crucial idea: a wave transfers **energy** (and information) from place to place, but **not matter**. A floating duck on ripples just bobs **up and down** — it does not travel across the pond. The wave moves through the water; the water itself stays put.
What does a wave transfer?
As a wave travels from one place to another, what does it carry with it?
- Energy (and information), but not matter
- Matter, carried along with the wave
- Both matter and energy equally
- Nothing — it just looks like it moves
Transverse waves 〰️
In a **transverse** wave the vibrations are **at right angles (perpendicular)** to the direction the wave travels. They have **crests** (peaks) and **troughs** (dips). Water waves and all **electromagnetic** waves (like light) are transverse.
Longitudinal waves 🔊
In a **longitudinal** wave the vibrations are **along (parallel to)** the direction of travel. Instead of crests and troughs they have **compressions** (particles squashed together) and **rarefactions** (spread apart). **Sound** is the key example.
Which are transverse?
Pick the TWO examples of TRANSVERSE waves.
- Ripples on water
- Light (an electromagnetic wave)
- Sound travelling through air
- A push travelling along a slinky spring
The parts of a wave 📏
Four measurements describe a wave: • **Amplitude** — the maximum displacement from the **rest** position (NOT crest to trough). • **Wavelength (λ)** — the length of one complete wave, e.g. crest to crest. • **Frequency (f)** — waves passing per second, in **hertz (Hz)**. • **Period (T)** — the time for one complete wave.
Label the wave
An interactive activity.
Match each quantity to its meaning
- Amplitude
- Wavelength
- Frequency
- Period
- Maximum displacement from the rest position
- The length of one complete wave
- The number of waves per second (Hz)
- The time for one complete wave
Frequency and period ⏱️
Frequency and period are two views of the same thing, and they are **reciprocals**: **T = 1 ÷ f** (period in seconds = 1 ÷ frequency in Hz). A wave of frequency 4 Hz has a period of 1 ÷ 4 = 0.25 s — a quarter of a second per wave.
Find the period
An interactive activity.
The wave equation 🟰
Speed, frequency and wavelength are linked by the **wave equation**: **v = f λ** (wave speed = frequency × wavelength; speed in m/s). It rearranges to f = v ÷ λ or λ = v ÷ f, so any one can be found from the other two.
Find the wave speed
An interactive activity.
Order the method
An interactive activity.
Find the wavelength
An interactive activity.
The wave rules
Waves transfer _____, not matter. In a transverse wave the vibrations are _____ to the direction of travel. The wave speed is found from v = frequency × _____.