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Page 1

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Newton
It was known that force
causes motion. Newton
clarified this by showing
that in certain
situations, force can
cause acceleration.

Page 2

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What is Force?
Force: That which
changes or attempts to
change the velocity or
shape of an object.
(The shape-changing
abilities of forces are
covered in the later topic
of Elasticity)

Page 3

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Force words
In mechanics, Forces
may also be labelled:
Effort, Load, Thrust,
Drag, Friction,
Reaction, Tension,
Compression, Weight,
and Centripetal.

Page 4

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Three Laws
Newton devised three
laws of motion ­ the
basis of Newtonian
Mechanics.

Page 5

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First Law
Every object continues
in a state of rest OR
uniform velocity in a
straight line unless
acted upon by an
unopposed (i.e.
resultant) force.

Page 6

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Implication
If you kick a ball and no
other force acts on it
(no friction, no weight ­
i.e. assume there is no
gravity) then it will
travel in a straight line
at the speed you kicked
it for ever.

Page 7

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Implication
Remember that equal
and opposite forces do
not just act on objects
at rest. They could be
acting on objects
moving at constant
velocity (e.g. when
Thrust = Drag)

Page 8

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Second Law
The rate of change of
momentum of an object
is directly proportional
to the applied force and
occurs in the direction
of the force.
This can be expressed
mathematically as...

Page 9

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Second Law




Where p is the
momentum, calculated
from (mass x velocity).

Page 10

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Second Law

=


Is only true if we
define a force of 1
Newton = 1kgms-2.

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