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

Acceleration

• An object can change its speed by:

  • speeding up

  • slowing down

• When an object speeds up, it is accelerating

• When an object slows down, it is decelerating

Calculating acceleration

Extended Tier Only

• When an object moves in a straight line, its acceleration can be defined as:

The change in speed per unit time

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

• The acceleration of an object often changes throughout an object's journey

• Therefore, it is often useful to know the average acceleration

$a=\frac{∆v}{∆t}$

• Where:

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

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

  • $∆t$ = time taken in seconds (s)

Formula triangle for acceleration, change in speed and change in time

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

 Change in speed

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

$∆v=v-u$

• Where:

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

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

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

• If an object speeds up, its acceleration is positive

• If an object slows down, its acceleration is negative

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

Acceleration of different objects

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