Velocity is the speed of an object in a given direction. If the body changes direction it changes velocity even if the speed stays the same.
- An object moving steadily round in a circle has a constant speed. Its direction of motion changes as it goes tound so its velocity is not constant.
- Two moving objects can have the same speed but different velocities. For example, a car travelling north at 30m/s on a motorway has the same speed as a car travelling south at 30m/s. But their velocities are not the same because they are moving in opposite directions.
If the velocity of a body changes, we say that it accelerates. We can calculate acceleration using the equation :
acceleration = change in velocity ÷ time taken for the change
The unit of acceleration is metres per second squared (m/s2).
If the value calculated for acceleration is negative, the body is decelerating - slowing down.
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