3 June, 2000
The Ping Puzzle
June 3, Saturday
That's the sound scientists were hoping to hear as they lowered the pinger over the side of the ship. When the pinger is in the water, it can tell scientists how far it is from the bottom of the ocean.
It works like this. The pinger is attached to a cable (thick wire) which is lowered down in the water by a winch. The winch operators slowly let the cable out, and heavy weights pull the pinger down to the bottom.
All this time, the pinger is making a pinging sound. It can be heard throughout the ship. Sensors on the underside of the ship record when each ping is emitted. They also record the time that the ping's echo returns from the bottom of the ocean. Because scientists know how fast sound travels through water, they can calculate how far away something is by knowing how long it takes the "ping" and its echo to be "heard" by the sensors.
Think of it like this. You are standing facing a cliff that is across the lake from you. You shout as loudly as you can: "HELLO!" Your ear hears the sound almost immediately. Four seconds later, you hear the echo: "HELLO!" If you know that sound travels 300 meters per second through air, you can figure out how far away the cliff is. Go ahead, try it. The answer is at the end of this entry.
Pingers are often attached to scientific equipment that is being lowered to the bottom of the ocean. With the help of the pinger scientists lowering this equipment can keep it from hitting the ocean floor. Does this always work? Click on Janice’s page to learn about what could happen!
By the way, did you know that sound travels through water five times faster than it does through air? That's because the molecules in water are packed more closely together than they are in air.
ANSWER TO THE ECHO QUESTION:
The cliff is 600 meters away from you. It takes 2 seconds for the shout to travel across the lake to the cliff, and 2 more seconds to get back to you.
DAILY DATA LOG (6/03/00):
Air Temperature: 0 degrees C / 32 degrees F
Clear skies, sunny
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