Transcript File - twynham a level pe

Learning Objective
Describe Newton's Laws and
apply them to movements
Inertia
 Reluctance of a body to change from its existing type
of motion is called inertia.
 When a body is at rest it is reluctant to do anything
 Set of weights
 Bowling ball- heavy
 Can not be gained or lost
 Mass determines inertia- greater mass = greater inertia
 Harder to change speed/ direction
Newton's First Law
(Law of inertia)
 A body continues in a state of rest or
motion in a straight line, unless
compelled to change that state by
external forces exerted upon it.
Application
 Will keep travelling at a constant velocity
 But in real life forces act upon things- friction and
gravity
 If an object is changing in velocity and/or direction
then a net external force must be acting on it.
 If it is not changing then the net external force is zero.
 Snooker ball example.
Newton's Second Law
(Law of Acceleration)
 The rate of change of momentum of a
body is proportional to the force
causing it and the change that takes
place in the direction in which the
force acts.
Momentum=Mass x Velocity
 Quantity of motion that a body possesses.
 Two rugby players same velocity different masses..
 Two rugby players same mass, different velocity..
 Downhill skier/rugby scrum have large
momentums
 Force is needed to change momentum of an object
 In most sports the mass of an object is assumed
constant so can be removed from the equation- so
change in momentum becomes change in velocity
 Rate of change in velocity is directly proportional to
the force causing the change
 The change will happen in the same direction of the
force
 Rate of change of velocity = Acceleration
Force x Mass x Acceleration
 Forces are vector- they have direction
 Acceleration will only happen whilst the force is being
applied to the object i.e. foot on ball
 In sport contractions of various muscles provide the
force.
Sprinter
 Sprinter on the starting blocks applies a force that
provides them with acceleration.
 The magnitude of acceleration is proportional to the
magnitude of force exerted.
 Direction of acceleration is dependent on direction of
force
 Force – muscles through foot.
Newton's Third Law
(Law of Reaction)
 To every action there is an equal and
opposite reaction
 In the second law we suggested that the sprinter
applies a force in order to accelerate and this force
determines the direction of acceleration. However the
force and acceleration appear to be in opposite
directions!
 This is due to the Third law
 In sport normally to do with the performer and the
ground.
 The sprinter exerts a force on the blocks, and there is
an equal but opposite force driving the sprinter
forwards; but the blocks are attached to the earth and
the earth has such a large mass compared with the
sprinter the acceleration given by the sprinter is
insignificant. However the force given to the sprinter
by the earth causes them to accelerate.
 Ground Reaction Force
Application of the Laws
Newton’s Laws
Application
Law of inertia
In a penalty kick the ball (body) will remain on
the spot (in a state of rest) until it is kicked by
the player (an external force is exerted upon it)
Law of Acceleration
When the player kicks (force applied) the ball
during the game, the acceleration of the ball
(rate of change of momentum) is proportional
to the size of the force, so the harder the ball is
kicked the further and faster it will go.
Law of Reaction
When a footballer jumps up (action) to win a
header, a force is exerted onto the ground in
order to gain height. At the same time the
ground exerts an upward force (equal and
opposite reaction) upon the footballer.
Can you give your own examples
in your sport??