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What is acceleration?

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Quick answer

Acceleration is how quickly an object's velocity changes — speeding up, slowing down, or changing direction. When you press a car's accelerator, you increase its velocity; braking is acceleration in the opposite direction (deceleration). Acceleration = change in velocity ÷ time taken. Its units are metres per second squared (m/s²).

Key things to understand

  1. Acceleration = change in velocity ÷ time taken. Its units are metres per second squared (m/s²).
  2. It happens whenever velocity changes — getting faster, slower, or turning.
  3. A force is what causes acceleration: Newton's second law says force = mass × acceleration (F = ma).
  4. Near Earth's surface, gravity accelerates falling objects at about 9.8 m/s².

People also ask

Is slowing down acceleration?
Yes. Any change in velocity is acceleration. Slowing down is acceleration in the direction opposite to motion, often called deceleration.
What causes acceleration?
A net force. By Newton's second law, the bigger the force (or the smaller the mass), the greater the acceleration: F = ma.
Can something moving at constant speed be accelerating?
Yes — if it's changing direction, like a car going around a bend or a planet orbiting the Sun, its velocity is changing, so it's accelerating.

Part of the guide: Cars, Trains, Planes & Ships →