Shout at a cliff and the sound comes back a moment later. That returning sound is an echo, and the short delay before it arrives is enough to measure how fast sound travels.
An echo is sound reflected from a hard surface. Because the sound travels to the surface and back, it covers twice the distance before it returns, so the speed is found from speed = total distance divided by time. In air sound travels at about 330 to 340 m/s.
An echo is sound that has been reflected from a hard surface. The sound travels to the surface and back, covering twice the distance to the surface before it is heard.
In air the speed of sound is about 330 to 340 m/s, far slower than light.
Set the distance to the wall and watch the pulse travel out and return, with the stopwatch climbing to the echo time.
Four quick checks. Each correct answer earns XP and lights this skill on your star map.
An echo is...
The speed of sound in air is closest to...
When you measure an echo from a wall, the sound travels a distance of...
Compared with its speed in air, sound travels...
The factor of two is the whole trick: the sound makes a round trip, so the path is twice the distance to the wall.
A student stands 85 m from a cliff and hears the echo of a clap 0.50 s later. Find the speed of sound.
In an echo the sound makes a round trip, so use twice the distance to the surface. Using only the one way distance halves the speed. And sound travels faster in liquids and solids than in air, which is the opposite of what many expect.
Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.
A ship sends a sound pulse to the seabed and hears the echo 0.40 s later. If sound travels at 1500 m/s in water, the depth of the seabed is...
A man claps and hears the echo from a wall 0.40 s later. Taking the speed of sound as 340 m/s, the wall is...
Why is the factor of two needed when finding speed of sound from an echo?
Echoes and the speed of sound are locked in. Keep the chain going.