Properties of Wave Pulses and Waves
Introduced| English |
|---|
| wave/weɪv/ |
| transverse wave/trænsˈvɜːs weɪv/ |
| longitudinal wave/ˌlɒŋɡɪˈtjuːdɪnl weɪv/ |
A stadium "Mexican wave" — people stay put, the wave races round
- In a Mexican wave, each fan just stands and sits — yet a wave sweeps around the whole stadium.
- No person travels with it; only the pattern moves.
- That's the heart of a wave 波: it carries energy from place to place, but not matter.
- Understanding this one idea unlocks sound, light and every ripple.
Waves carry energy, not matter
- A wave is a disturbance that travels, moving energy without moving the medium along with it.
- A single bump is a pulse; a repeating disturbance is a continuous wave.
- Drop a stone in a pond: the ripple spreads outward, but the water just bobs up and down.
- The floating leaf goes up and down, not outward — proof that matter stays put.
A travelling wave carries:
A wave transfers energy; the medium only vibrates in place.
As a water wave passes, a floating leaf mostly bobs up and down rather than travelling with the wave.
The medium vibrates in place; the leaf shows the matter does not travel with the wave.
Transverse and longitudinal
- In a transverse 横波 wave, the medium vibrates perpendicular to the direction of travel (light, water ripples).
- In a longitudinal 纵波 wave, it vibrates along the direction of travel (sound, a pushed slinky).
- Both move energy forward, just with different particle motions.
- Only transverse waves can be polarised (lesson 14.3).
Transverse or longitudinal
Switch between transverse and longitudinal and watch how the particles move relative to travel.
In a transverse wave, the medium vibrates:
Transverse means the vibration is perpendicular to the travel direction.
Sound is a longitudinal wave.
Sound vibrates the air along the direction of travel — longitudinal.
Select all true statements about waves.
Waves transfer energy, come in transverse and longitudinal kinds — but never carry the medium along.
Speed depends on the medium
- A wave's speed is set by the material it travels through, not by how it was made.
- Sound travels faster in water than in air, and faster still in steel.
- Light travels fastest of all in a vacuum, slowing in glass or water.
- Change the medium and the speed changes; the frequency stays the same (set by the source).
A wave's speed is set by the ____ it travels through.
The medium (air, water, steel) sets the wave speed.
A wave transfers energy, not matter. The medium (water, air, the crowd) only vibrates in place — it does not travel along with the wave. Confusing the moving pattern with moving matter is the classic wave misconception.
You flick one end of a long rope up and down once, sending a pulse along it.
- The pulse (and its energy) travels to the far end.
- Each bit of rope only moves up and down — it does not slide toward the other end. That is a transverse wave.
A wave carries energy, not matter — the medium only vibrates in place. Transverse waves vibrate across the direction of travel (light, ripples); longitudinal waves vibrate along it (sound). A wave's speed is set by its medium.