Energy from sound
Beneath the fishing boat there are thousands of fish waiting to be
caught. The crew on the boat can’t see the fish—but they know the fish
are there. How can they tell?
There is a special kind of \”whistle” that can help people find fish.
It’s ultrasound— sound that is higher than any sound your
ears can hear. Ultrasound can be used underwater to find things that
people can’t see.
All sounds—even the ones you can’t hear— are actually bunches of
tiny pushes and pulls. Those pushes and pulls make waves that can travel
through things like water, air, and even the ground. The waves are a
kind of energy—sound energy.
The \”whistle” that finds fish is made by a special machine called a
sonar (SOH nahr). The sonar sends ultrasound waves through the water in
a narrow beam. It makes the beam sweep in a big circle around the boat.
Whenever the beam of ultrasound hits something, it bounces back to the
sonar. Then the sonar signals that there is something in that spot.
Usually the signal shows the bottom of the lake or river. But once in a
while the beam hits something else.
The \”something” in that spot could be rocks, a bed of seaweed, or fish.
Rocks and
seaweed stay in one place, so the signal from a rock pile or a seaweed
bed always stays the same. But fish move—so a signal that keeps
changing almost always means a school of swimming fish!
Of course, ultrasound won’t make the fish bite on a hook or swim into
the net of a big fishing boat. But it shows where the fish are—and it
makes your chances for a fish dinner a lot better!
