Bats and sonar

The idea

Echolocation is locating objects by sensing echoes of emitted ultrasonic waves; sonar applies the same principle, sending ultrasonic waves into water and analysing the reflections to find objects' distance, direction and speed.

Flying in the dark

A bat flies at night and does not bump into walls or trees. It finds its prey in the dark.

How do you think the bat finds its way?

• It sends out sound and senses the echoes
• It sees by the light of its own eyes in the dark
• It feels the air with its wings

Send a signal

A ship sends an ultrasonic signal into seawater, where sound travels at 1530 m s⁻¹. Choose how long the signal takes to come back.

Locating with echoes

Bats emit short bursts of ultrasonic waves and sense the echoes from nearby objects. This is echolocation. Humans use the same idea in sonar, which sends ultrasonic waves into water.

Echolocation is locating objects by sensing the echoes of emitted ultrasonic waves. Sonar uses the same principle: ultrasonic waves are sent into water and the reflections are analysed to find an object's distance, direction and speed.

Notes

Echolocation locates objects by sensing echoes of ultrasonic waves. Sonar sends ultrasonic waves into water to find an object's distance, direction and speed.

Check yourself

What is echolocation?

How does a bat find obstacles and prey in the dark?

What does sonar stand for, and what does it use?

A sonar signal sent into seawater returns after 0.60 s. The speed of sound in seawater is 1530 m s⁻¹. How far is the object, in m?

Answer: 459 m

The signal reaches the object in 0.60 ÷ 2 = 0.30 s. Distance = 1530 × 0.30 = 459 m.

• Locating objects using reflected sound waves — correct. Yes!
• Locating objects using the light that they reflect. Echolocation uses reflected sound waves, not light.
• Making a loud sound by rapid expansion of gases. That makes a sudden loud sound. Echolocation is locating objects using reflected sound waves.
• It listens for the echoes of the sounds that humans make. Most bats emit short bursts of ultrasonic waves themselves and sense the echoes.
• It emits short bursts of ultrasonic waves and senses the echoes — correct. Yes!
• It uses infrasonic waves below 20 Hz. Bats emit ultrasonic waves, which have a frequency above 20 kHz.
• Sound navigation and ranging, using light sent into the air. Sonar sends ultrasonic waves into water and analyses the reflections.
• Sound navigation and ranging, using ultrasonic waves sent into the air. Sonar sends ultrasonic waves into water and analyses the reflections.
• Sound navigation and ranging, using ultrasonic waves sent into water — correct. Yes!