Acceleration
Learning Objectives:
Keywords: Velocity, Acceleration, Time, Graph
Acceleration is the rate of change of velocity. It is the amount that velocity changes per
unit time.
Acceleration =change in velocity
time taken
If an object accelerates from an initial velocity (u) up to a final velocity (v) then the
average acceleration of an object can be calculated using the equation:
α=v−u/t
This is when:
- u) is measured in metres per second (m/s)
If an object is slowing down, it is decelerating (and its acceleration has a negative
value).
Example
A car takes 8.0 s to accelerate from rest to 28 m/s. Calculate the average acceleration
of the car.
The acceleration in free fall due to the Earth’s gravity is 10 m/s2, g = 10 m/s2
Velocity-time graphs
Determining acceleration
For a moving object, the velocity can be represented by a velocity-time graph.
A horizontal line on a velocity-time graph, shows that the object is at constant velocity,
but a sloping line on a velocity-time graph, shows that the object is accelerating.
The gradient of the line is equal to the acceleration of the object.
The table shows what each section of the red line on the graph represents
Section of graph
A
B
C
D (v=0)
Gradient
positive
zero
negative
zero
Velocity
increasing
constant
decreasing
stationary (at rest)
Acceleration
positive
zero
negative
zero