Same speed but different velocity
The diagram shows three aircraft taking part in a display.
1. What is the same about the motion of the planes?
2. What is different?
All three aircraft have the same speed, but they are moving in different directions. We say that they have differnt velocities. Velocity is speed in a given direction.
Acceleration
When your velocity changes, we say that you accelerate. Racing drivers want a very large acceleration. This means they want to go from a low speed to a high speed in a very short time.
How to calculate acceleration
The racing car in the figure takes 5 seconds to reach a velocity of 50 metres per second. So every second, its velocity increases by 10 metres per second. This is its acceleration. You can work out acceleration like this:
acceleration = change in velocity/time taken
So for the racing car, acceleration = 50m/s / 5s = 10m/s2
The change in velocity is measured in metres per second. the time taken is measured in seconds. So the units of acceleration are metres per second, per second.
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