When acceleration is directly proportional to displacement, you have Simple Harmonic Motion (SHM)

Each of the two balls is moving in SHM. Concentrate on the left ball, the green graph is measuring its displacement.

Imagine a vertical line through the centre of the three coloured lines, notice how whenever the green displacement is to the right of the line the red acceleration is to the left, and visa versa. Acceleration and displacement are always in opposite directions.

lesson notes: 02-simple-harmonic-motion

audio: 02 simple harmonic motion

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