In the above animation, five points on the wave are considered for the explanation. The fully interactive applet is given below for you to practise. The phase of a point implies its direction of vibration on a wave. For example, both points A and E vibrate exactly the same way are said to be in phase: when A goes up so does B; the phase difference is either 0 0 or 360 0 . If you consider the motion of points A and C, on the other hand, when A goes down C goes up or vice versa. Therefore, A and C are said to be out of phase; the phase difference is 180 0 . That means the phase difference between two points on a wave - or two waves for that matter - can take any value between 0 0 and 360 0 . The phase difference between points A and B, for instance, is 90 0 . From the above examples, it is clear there is a connection between the path difference between two points - or two waves - and phase difference. It is as follows: Phase difference = (path difference / wavelength) x 360 φ = x
The above shows how a column of liquid of density ρ can be made to oscillate while undergoing SHM, simple harmonic motion. When you blow gently into the tube at one end, the excess weight of the column of height, x, pushes the rest of the liquid down with a force that results in an downward acceleration. It can be shown that the acceleration of the liquid in the column in question is proportional to the negative displacement. Therefore, the motion of the liquid is simple harmonic. If you want to learn more about the simple harmonic motion - proofs and worked examples - please follow this link below: Simple Harmonic Motion Tutorial with Simulations
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