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Sound is the energy produced by vibrations. When an object vibrates, sound waves travel through the air and reach a person's ears. Sound Waves are longitudinal waves (waves where the displacement of the medium is in the same direction as or the opposite direction to the direction of propagation of the wave) that can only move via air. That means sound cannot be heard in space, and are more likely to be heard underwater than in the atmosphere. The speed of sound is much slower than the speed light at 343 meters per second,[1] which is why lightning in a thunderstorm is always seen before a clap of thunder.

The volume of the sound being heard depends on the height the crests of the sound waves. The volume of sounds are measured by decibels (dB):

Decibel Comparison
Number of decibels (dB) Comparable to
10 Needle hitting a flat surface
25 Whispering
50 Talking
75 Vacuum Cleaner
100 1 meter away from loudspeaker
Threshold of pain (130 dB)
150 Fireworks
300 Krakatoa eruption (loudest recorded historical sound)
1,100 The creation of a black hole larger than the observable universe


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