ACCELERATION

Acceleration - the rate of change in speed (m/s2)

� 1 m/s2 means that the object is increasing its speed

1 m/s every second

a = ∆ v

∆ t

or

a = vf – vi

∆ t

Average acceleration - average rate of change in speed

of an object

Constant acceleration - the same rate of change is

occurring through each time interval. (second, minute or

hour)

Note: If the object has a positive acceleration, the object is “speeding up”. If the object has a negative acceleration, the object is “slowing down”.

Example 1:

Olympic gold medallist Kerrin Lee-Gartner is moving at

1.8 m/s near the top of a hill. 4.2 s later she is travelling

at 8.3 m/s. What is her average acceleration?

v1 = 1.8 m/s ava =

2 1v v

t

−

∆

∆t = 4.2 s

v2 = 8.3 m/s (8.3 1.8) /

4.2av

m sa

s

−=

aav = ? = 1.5 m/s2

Kerrin Lee-Gartner’s average acceleration is 1.5 m/s2.

Example 2:

In a race, a car traveling at 100 km/h comes to a stop in

5.0 s. What is the average acceleration?

v1 = 100 km/h ava =

2 1v v

t

−

∆

v2 = 0 km/h

∆t = 5.0 s (0 100) /

5.0av

km ha

s

−=

aav = ? = -20 km/h/s

The average acceleration of the car is -20 km/h/s.