The Speed Sound
Solids transmit(传递)sound very well. Try holding a wooden stick against part of a machine, and place your ears against the stick. The movement of the ball-bearings(滚珠轴承)can be clearly heard. This is a good way of finding the exact source of trouble in a motor-car engine which sounds as if it is wrong and yet gives no information of where the trouble is.
It is probably a good thing that sound cannot travel through a vacuum, for we are thus limited to earthmade sounds. The violent disturbances which are seen occasionally in the sun, for example, may affect our magnetism(磁力)and our radio;they do not affect our ears, which is a very good thing for our peace of mind.
If we have used our eyes and ears, we may have realized that sound takes time to travel through the air. The sound of thunder nearly always follow the lightning flash although they happen at exactly the same time. And the appearance of white cloud above a distant ship or train tells us, before anything is heard, that its whistle has sounded. Just how fast does sound travel through the air?
The speed of sound in the air at ordinary temperature is about 1, 100 feet per second, which is about one mile in five seconds or about 700 miles per hour. The speed of sound increases slightly with a rise in temperature and falls with a decrease in temperature. It is not affected by the pressure of the air.
16 “How Fast Sound Travels” can replace the original title of the passage.
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17 We never hear anything that happens on the sun because of the distance between the earth and the sun.
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18 The sound of thunder always follows the lightning flash because the sound of thunder travels more slowly through the air.
A Right B Wrong C Not mentioned
19 The research of sound is important to us.
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20 The speed at which sound travel through the air at ordinary temperature is about 1, 100 feet per minute.
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21 Our eyes are keener than our ears.
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22 The speed of sound increases with a rise in temperature.
A Right B Wrong C Not mentioned
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