Idea 5of 9Builds onHow longHow often
The medium sets the speed
Shake faster. Does the wave go faster?
Today you'll discover
- who decides how fast a crest travels
- the see-saw between how often and how far apart
- the one equation that ties them
Think firstShake the rope twice as fast. The crests…
You shake the rope twice as often. How fast does each crest travel now?
Predict first, then drag the dial. Watch the speed readout stay put while λ changes.
A wave on a rope with its wavelength bracketed. After a prediction, the rope is redrawn with crests half as far apart, then the wave-speed bench opens with a frequency slider, a wavelength readout and a fixed speed readout. The last step asks what happens when a wave crosses into a faster rope.
See the whole ideathe big idea and the key word, in one place
The big idea
The medium sets the speed, so f and λ trade.
Easy to get wrongShaking faster does not make a wave travel faster. It makes more crests, packed closer, at the same speed.
Key word
- wave equation
- v = f λ: a wave's speed is its frequency times its wavelength; the medium fixes v
About this modelThe pattern travels; the particle only bobs. One square of the drawing is 0.5 m.
The pattern travels; the particle only bobs. One square of the drawing is 0.5 m.
Ready to use it?
- Use v = f λ to find any one of the three from the other two.