A ripple sets out across a pond. Its crest passes a floating leaf, and 2 s later it reaches a dock post 6 m farther on.
How fast is the ripple? The travel is already measured: 6 m in 2 s. A wave's speed is found the way any speed is found.
Pick one crest and follow it. The crest is the moving thing here.
The crest travels 6 m in 2 s, so its speed is 6 ÷ 2 = 3. The ripple's speed is 3 m/s.
This is not a new equation. It is the same speed = distance ÷ time used for every moving object since earlier grades, applied to a new moving thing: the crest of a wave.
For a longitudinal wave, there is no crest to watch, so follow one compression instead. The distance a crest or compression travels each second is the wave's speed.
The thing followed is always the pattern, never a piece of the medium. The water stays in the pond; the crest shape is what crosses it.
A wave crest on a lake travels 12 m in 3 s. Calculate the wave's speed.
Write down the values:
distance = 12 m, time = 3 s, wave speed = ?
Write down the equation:
wave speed = distance ÷ time
Substitute in the values, and calculate:
wave speed = 12 ÷ 3 = 4
The wave's speed is 4 m/s.
A compression travels 9 m down a stretched spring in 1.5 s. Calculate the wave's speed.
Write down the values:
distance = 9 m, time = 1.5 s, wave speed = ?
Write down the equation:
wave speed = distance ÷ time
Substitute in the values, and calculate:
wave speed = 9 ÷ 1.5 = 6
The wave's speed is 6 m/s.
Griet times a ripple crest crossing a swimming pool. It travels 10 m in 4 s. Enter the wave's speed, in m/s.
A wave travels along a rope from Hale's hand to a door handle. To find the wave's speed, which distance is divided by the time?
Eirik says: 'A wave's speed tells how far a crest travels each second.' Is Eirik correct?
A storm wave's crest travels 42 m across a bay in 12 s. Enter the wave's speed, in m/s.
A compression travels down a long spring stretched across a gym floor. Which measurement pair gives the wave's speed?
A ripple crest crosses a 45 m pond in 9 s. Enter the wave's speed, in m/s.