Download Newton`s Laws of Motion

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Newton’s Laws of Motion
Linear Kinetics
Newton’s First Law of Motion
• Law of Inertia
Every body will remain in a state of
rest or constant motion (velocity) in a
straight line unless acted on by an
external force that changes that state
• A body cannot be made to change
its speed or direction unless acted
upon by a force(s)
• Difficult to prove on earth due to the
presence of friction and air
resistance
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Newton’s Second Law of Motion
• Law of Acceleration
A force (F) applied to a body causes an
acceleration (a) of that body which has a
magnitude proportional to the force, and takes
place in the direction in which the force acts
• Vitally important in sport as it forms the link
between force and motion:
• Force = mass
• F=m
acceleration
a
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Applications of Newton’s 2nd Law
• Assuming mass
remains constant, the
greater the force the
greater the
acceleration
• What is the
acceleration of the ball
(ball mass = 1.5 kg)?
F = 500 N
F=m
a=?
a
F
500
=
∴a =
m
1.5
a = 333 m·s-2
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Newton’s Third Law of Motion
• Law of Reaction
For every force that is exerted by one body on a
second body there is an equal (magnitude) and
opposite (direction) simultaneous force exerted by
the second body on the first
• Therefore every force which is applied by a body is
accompanied by a reaction force on that body
• Difficult to visualise but can be felt:
– e.g. In boxing the force applied by a punch is
experienced by the opponent’s chin and the puncher’s
hand
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Examples of Newton’s 3rd Law
• Ground Reaction Force
(GRF) is a special type
of force explained by
Newton’s 3rd Law of
Motion
• Equal in magnitude and
opposite in direction to
the force applied to the
ground by the body
• Needs to be considered
separately in horizontal
(friction) and vertical
(normal) directions
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Summary
• Newton’s Law of Gravitation
– Attractive forces exist between bodies (e.g. a body and the Earth)
that are proportional to the product of their masses and inversely
proportional to the distance between them
• Newton’s First Law (Inertia)
– A force is required to accelerate (i.e. change the velocity of) a body
• Newton’s Second Law (Acceleration)
– The acceleration of a body is proportional to the sum of the forces
acting on it
• Newton’s Third Law (Reaction)
– Any body that applies a force to another body experiences a
simultaneous reaction force that is equal in magnitude and opposite
in direction to the applied force
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