Bat Sonar
Bats hunt in the dark by shouting and listening for echoes. Send a ping, watch it bounce back and use the echo time to find out how far away the wall or moth is.
- Speed of sound
- 343 m/s
- Timer
- 0.0 ms
- Echo time
- Waiting…
- Distance found
- ?
The maths, live
Speed in air v = 331 + 0.6 × Tv = 331 + 0.6 × 20 = 343 m/sDistance d = v × t ÷ 2Send a ping to measure tWe divide by 2 because the sound goes there and back. Real bats can hear echoes from a moth a few metres away in just a few thousandths of a second!
How it works
A bat sends out a short, very high-pitched call. The sound spreads out at the speed of sound, about 343 m/s in air at 20 °C, hits an object and bounces back as an echo. The bat measures how long the echo takes to return.
The sound travels to the object and back again, so the distance is the speed times the time, divided by 2: d = v × t ÷ 2. The speed of sound changes a little with temperature (v ≈ 331 + 0.6 × T), so warm air carries the ping slightly faster. Ships and submarines use the same idea, called sonar.
Try this
- Put the wall 10 m away. How long does the echo take?
- Double the distance. What happens to the echo time?
- Make the air colder. Does the echo come back sooner or later?