Properties of Wave Pulses and Waves
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| wave/weɪv/ | sóng |
| transverse wave/trænsˈvɜːs weɪv/ | sóng ngang |
| longitudinal wave/ˌlɒŋɡɪˈtjuːdɪnl weɪv/ | sóng dọc |
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:
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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.
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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:
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Transverse means the vibration is perpendicular to the travel direction.
Sound is a longitudinal wave.
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Sound vibrates the air along the direction of travel — longitudinal.
Select all true statements about waves.
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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.
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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.
Write from a cork that rises 4 cm
- A water wave travels 12 m past a cork.
- The cork rises 4 cm and returns. Say what moved 12 m.
A wave on water travels 12 m past a floating cork. The cork rises 4 cm and falls back to where it started. What has moved 12 m, and what has the cork done?
The cork oscillates in place while the wave moves on.
What travelled 12 m?
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The cork only oscillated through 4 cm.