2 Kinematics - BC Science Physics 11

2.2 Acceleration
Warm Up
Below are two blank speed-time graphs.
On graph (a), sketch the slope that represents a sports car traveling at constant speed.
On graph (b), sketch the slope of the same car starting from rest and speeding up at a constant rate.
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Changing Velocity
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48 Chapter 2 Kinematics © Edvantage Interactive 2012 ISBN 978-0-9864778-3-6
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Whenever the velocity of an object changes, the object experiences acceleration.
Acceleration is a change in velocity over a period of time:
acceleration = change in velocity
change in time
The symbol for acceleration is a. Velocity has the same symbol as speed, which is v.
If the velocity at the start of the time interval is v 0 , and at the end of the time interval is v f ,
then the change in velocity will be v f – v 0 . If the time at the beginning of the time interval
is t 0 , and the time at the end of the time interval is t f , then the change in time, the time
interval, is t f – t 0 . Using these symbols, acceleration can be defined as:
a = v f – v 0
t f – t 0
or a = ∆v
∆t
where the ∆ symbol is shorthand for “change in” or “interval.”
Since velocity has two aspects to it, both speed and direction, acceleration can
occur under three conditions:
(a) if speed changes,
(b) if direction changes or
(c) if both speed and direction change.
The standard unit for expressing acceleration is m/s 2 . An object is accelerating at a
rate of 1 m/s 2 if its speed is increasing at a rate of 1 m/s each second.