Radar (noun, “RAY-dar”)
This is a system people use to detect where something is, where it’s going and how fast it’s moving. Radar has a transmitter that produces radio waves and a receiver that detects them. The system first sends out radio waves. The waves hit an object and some get reflected back toward the radar. As they return, the waves are picked up by the radar’s receiver. The time that it takes for the waves to come back and how the waves have changed when they return provides useful information about the object ahead.
The word “radar” comes from the U.S. Navy. It was an acronym — or a word made out of the starting letters from a group of words. RADAR stood for RAdio Direction And Ranging. But now it’s been used so much that “radar” is a word on its own.
In a sentence
Scientists can use radar to find out how deep the ocean is — taking measurements that are accurate to within one centimeter (0.39 inch).
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