Acceleration — Physical education, 14–17
Acceleration tells us how quickly velocity changes. It is not only about going faster: slowing down or changing direction also counts.
What acceleration means
Acceleration is a change in velocity over time. A car accelerates when it speeds up, slows down, or turns, because velocity includes direction as well as speed. A steady speed on a straight road means zero acceleration, even though the car is moving.
Why measure it?
Knowing acceleration lets us predict where an object will be and how fast it will move later. People needed this for vehicles, falling objects, and machines, so experiments compared changes in velocity with the time taken. The useful rule is acceleration = change in velocity ÷ time.
A bicycle speeding up
A cyclist’s velocity rises from 4 m/s to 10 m/s in 3 s. First find the change: 10 − 4 = 6 m/s. Then divide by the time: 6 ÷ 3 = 2 m/s². The cyclist’s acceleration is therefore 2 m/s², meaning the velocity gains 2 m/s every second during this interval.
The common mix-up
A common mistake is to call every moving object accelerated. That feels reasonable because “accelerate” sounds like “move”. In physics, acceleration means that velocity changes, so a train travelling straight at a constant 20 m/s has no acceleration, while a car turning at constant speed does.
Where it is used
Car safety systems measure acceleration to detect a crash and trigger airbags quickly. Sports scientists use it to compare a sprinter’s start or a cyclist’s climb. These measurements are useful because forces on people and equipment depend strongly on how quickly motion changes.
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