Newton’s Laws of Motion
There is a direct link between motion and force, which can be
stated as, ‘without force there can be no motion’.
Newton’s First Law of Motion (Law of Inertia)
‘A body continues in a state of rest or of uniform velocity unless
acted upon by an external force.’
Consider a football on the penalty spot. A body (the football)
continues in a state of rest (on the penalty spot) unless acted upon
by an external force (the muscular force generated by the kick).
Newton’s Second Law of Motion (Law of Acceleration)
‘When a force acts upon an object, the rate of change of
momentum experienced by the object is proportional to the size of
the force and takes place in the direction in which the force acts.’
Again consider the football during the penalty kick. When a force
acts upon an object (the muscular force applied by the leg) the rate
of change of momentum experienced by the object (the
acceleration of the ball) is proportional to the size of the force (the
ball will accelerate faster with greater force in the kick) and takes
place in the direction in which the force acts (the ball accelerates
towards the goal).
Newton’s Third Law of Motion
‘For every action there is an equal and opposite reaction.’
This is saying that whenever an object exerts a force on another,
there will be an equal and opposite reaction exerted by the second
on the first.
Consider a rugby player swerving to the right to avoid a tackle. For
every action (the rugby player pushes the ground to the left with
their feet) there is an equal and opposite reaction (the ground
exerts an equal force to the right allowing the player to swerve in
that direction).