Acceleration (AQA GCSE Physics) : Revision Note

Acceleration

Defining Acceleration

• Acceleration is defined as the rate of change of velocity

• In other words, it describes how much an object's velocity changes every second

• The equation below is used to calculate the average acceleration of an object:

• Where:

  • = acceleration in metres per second squared (m/s²)

  • = change in velocity in metres per second (m/s)

  • = time taken in seconds (s)

• The change in velocity is found by the difference between the initial and final velocity, as written below:

change in velocity = final velocity − initial velocity

• Where:

  • = final velocity in metres per second (m/s)

  • = initial velocity in metres per second (m/s)

• The equation for acceleration can be rearranged with the help of a formula triangle as shown:

Acceleration, change in velocity, and time formula triangle

Speeding Up and Slowing Down

• An object that speeds up is accelerating

• An object that slows down is decelerating

• The acceleration of an object can be positive or negative, depending on whether the object is speeding up or slowing down

  • If an object is speeding up, its acceleration is positive

  • If an object is slowing down, its acceleration is negative (sometimes called deceleration)

• Two examples of accelerating and decelerating objects are shown in the image below

A rocket speeding up (accelerating) and a car slowing down (decelerating)

Estimating Accelerations

• The acceleration of an object is a measure of how quickly its velocity changes

• A typical family car, for example, takes around 10 seconds to go from 0 m/s to 27 m/s (roughly 60 mph)

  • This is an acceleration of about 2.7 m/s²

  • The table below gives some other typical accelerations:

Typical Accelerations Table