A particle that moves uniformly in a circular path is accelerating yet moving at a constant speed. Explain this statement.

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Acceleration is a change in velocity over time. Velocity is different to speed, because it has a direction (for example a car moving at 10 mph along a road heading north will have a greater velocity due north than a car moving at 10 mph along a road heading north-east).

A particle moving in a circular path is constantly slightly changing its direction. Therefore its velocity is changing, and as a result so is its acceleration. If we take the particle to be a satellite and the circular path to be the orbit around the earth, the satellite is constantly accelerating towards the centre of the earth, like an object in free fall. However its forward velocity balances out the downward acceleration, which causes it to move in a circular path around the earth. The downward acceleration brings it lower only as much as the curvature of the earth itself. 

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