Acceleration (Cambridge (CIE) IGCSE Physics): Revision Note

Acceleration

Extended tier only

• Acceleration describes how the velocity of an object changes over time

• Acceleration is defined as:

The change in velocity per unit time 

• In other words, acceleration is the rate of change of velocity

• The equation for calculating acceleration is:

$a=\frac{∆v}{∆t}$

• Where:

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

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

  • $∆t$ = time taken in seconds (s)

To use a formula triangle, simply cover up the quantity you wish to calculate and the structure of the equation is revealed

 Change in velocity

• The change in velocity is the difference between the initial and final velocity:

$∆v=v-u$

• Where:

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

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

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

Speeding up and slowing down

• An object can change its velocity in several ways:

  • speeding up

  • slowing down

  • changing direction

• Any change in an object's velocity is an acceleration

  • When an object changes direction, it is accelerating

• Acceleration is positive if its direction is in the same direction as the motion of the object

• When an object speeds up, it is accelerating

  • This is positive acceleration

• When an object slows down, it is decelerating

  • This is negative acceleration

Acceleration of different objects

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