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Physics - Waves and Periodic Motion

There are two kinds of waves, transverse and longitudinal. In a transverse wave, the medium moves in a direction perpendicular to the movement of the wave. In a longitudinal wave, the medium moves in the same direction as the wave. 

Period, Frequency, Wave Length and Amplitude 

Think about a transverse wave. When we talk about the period of this wave, we’re talking about the amount of time it takes the wave to move through one complete cycle from peak to peak or from trough to trough. If it takes 3 seconds for the wave to get from peak to peak or from trough to trough, then the wave has a period of 3 seconds. 

When we talk about the frequency of a wave, we are talking about the number of complete cycles it produces in 1 second. So, if a wave has a period of 3 seconds, it goes through one cycle in 3 seconds which means it goes through 1/3 of a cycle in a second. Its frequency is 1/3 of a cycle per second. Frequency is measured in the unit hertz and one cycle per second equals 1 hertz. 

Rule Number 38: 
For any wave, frequency equals one over period and period equals one over frequency. A wave’s wavelength is the distance from crest to crest or from trough to trough. So, a long wavelength corresponds to a low frequency. Wavelength is measured in meters or other units of length. If you know the wavelength and the frequency, you can figure out how fast the wave is moving. 

Rule Number 39 
A wave’s velocity equals frequency times wavelength.