Forces and Motion

Calculations for Acceleration.

Acceleration = Change in Velocity ÷ Time.

This equation is important!

a = (v-u) ÷ t

where a = acceleration
v = final velocity (the one it ended up with)
u = initial velocity (the one it started with)
t = time

1.  If a car changes from 10 m/s to 30 m/s in 8 seconds,
what is its acceleration?

v = 30
u = 10
t = 8

       a = (30 - 10) ÷ 8
= 20 ÷ 8
   = 2·5 m/s2

2. If a bicycle moving  at 15 m/s takes 10 seconds to stop,
what is its acceleration?

In this example, the final velocity is zero because the bicycle has stopped.

v = 0
u = 15
t = 10

       a = (0 - 15) ÷ 10
= -15 ÷ 10
   = -1·5 m/s2

The acceleration is negative because the bicycle has slowed down.

Acceleration is the rate of change of an objects velocity.
The object is said to have constant acceleration
if it gets faster (or slower, or its direction changes) at the same rate.

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