How Do We Hear?
Sound is a form of energy. It is produced when the molecules of air vibrate. Vibration is the back and forth movement of air that makes sound. When air particles vibrate, energy is passed from one particle to another. This is how a sound wave travels. We can hear sounds that are both close up and far away. If the sound wave reaches our ears, we will hear the sound. Volume tells if a sound is loud or soft. Pitch of sound tells how high or low it is. Light travels faster than sound. The speed of light is 671 million miles per hour. The speed of sound is 761 miles per hour. That’s why you see a flash of lightning before you hear the thunder.
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The correct answer is
The smallest number is the one that comes first while counting.
To arrange the given numbers in order from smallest to greatest, find the smallest number among all the given numbers.
21 is the smallest number.