Electromagnetism, Properties Of Waves, Motion, Gases & The Kinetic Theory Worksheet With Answers Page 16
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36Unit 3 –Motion
The equations
Speed is defined as the distance moved per unit time, and hence, the equation for
speed is :
Distance is measured in
metres (m)
speed = distance
Time is measured in
seconds (s)
time
Speed is measured in
metres per seconds (m/s)
If the speed is not constant this equation can still be used, but it gives a value for the
average speed.
There are also equations for objects that are accelerating, e.g.
acceleration = change in speed
a
= v - u
time
t
v = u + at
Re-arranging
If the acceleration is constant, then there are 3 other equations that we can use. These are
known as the ‘equations of motion’ or ‘kinematic equations’, and are all given in the
examination :
= ( u + v ) t
x
v = u + at
2
2
= ut + ½ a t
x
2
2
v
= u
+ 2a
x
Symbol
Quantity
Unit
=
distance/displacement
m
x
u
=
initial velocity
m/s
v
=
final velocity
m/s
2
a
=
acceleration
m/s
t
=
time
s
All the above quantities, except for ‘time’, are vectors, meaning that they must have a
direction. For example, displacement is simply the ‘straight line’ distance between the
start and end point of your journey, in a certain direction.
16
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