#### Transcript Slide 1

```By Cade and Georgia
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Newton’s laws of motion, including an understanding
of force, mass and weight, acceleration and inertia
applied to sport and physical activities
The principles of conservation and transfer of
momentum, impulse and sequential and/or
simultaneous force summation applied to sport and
physical activities
Angular motion including torque, angular velocity,
momentum and moment of the inertia and their
application to sport and physical activities
Elasticity and the coefficient of restitution of sports
equipment and the effect of rebound velocity on
performance.
An object will remain in a state of rest or constant
motion unless acted upon by an external force.
Inertia is a tendency for a body to resist change in
its state of motion, whether that be at rest or
moving with a constant velocity. It is harder to
move or change the state of motion of an object if it
has a greater amount of inertia which is directly
related to its mass. The more massive an object the
greater its inertia will be. For example the amount
of force required to move a 100kg barbell is going
to be greater than the force required to move a 5kg
barbell.
Mass and weight are two different quantities that
are often used interchangeably. Mass is the
amount of matter that makes up an object
where weight is the measure of gravitational
force acting on a body. In example what we are
made up of is said to be mass and weight is the
mass multiplied by the acceleration due to
gravity.
Force is a push or pull acting on an object. Some examples of this is when you
kick a ball, the force of gravity ,which is the downward pull, pulling the
ball back towards the ground.
The different types of forces are friction, gravity, weight, air resistance and
water resistance.
Friction is a force that occurs when two surfaces come in contact with each
other, the friction force opposes the motion of an object.
Gravity is the downward pull generated by the earth constantly spinning.
Air and Water resistance is the amount of air/ water slowing down an object
during its motion.
Newton had 3 different laws of motion. First one was the law of
inertia, second one being the law of acceleration and the third law
is the law of action – reaction.
The first law is an object will remain in a state of rest or constant
motion unless acted upon by an external force. (Explained more in
slide 3)
The second law is a force applied to an object will produce a change in
motion (acceleration) in the direction of the applied force that is
directly proportional to the size of the force.
The third law is for every action there is an equal and opposite
reaction, for example in tennis, when a tennis ball is hit the force
applied by the racquet to the ball is obvious to see because the ball
changes direction and accelerates. The reaction force of the ball on
the racquet is more difficult to see, this is because the racquet has
greater mass then the tennis ball and the change in its acceleration
is very small.
Momentum is a measure of the amount of motion
that an object has. The momentum of an object
is directly related to its mass and its velocity.
Momentum is equal to the mass of the object
multiplied by the velocity of the object and has
the units kg m/s:
momentum= mass x velocity
Momentum is conserved in an isolated system,
which is one where there are no external forces
acting. The principle of conservation of
momentum states the total momentum of the
system before the collision is equal to the total
momentum after the collision. An example is
the effects of air resistance and friction, for
example, would be present, but they can be
ignored in the order to qualitatively determine
changes in momentum.
Angular momentum is the quantity of angular
motion of an object. It is a product of moment
of inertia and angular velocity of an object
rotating around an axis. It applies to Newton’s
first law of motion. The formula to calculate the
moment of inertia is:
moment of inertia= mass x radius2
Angular motion is conserved when the body is in
flight. This principle is useful to understand when
analysing human movement in activities such as
diving, trampolining and gymnastics.
Summation of momentum
When the main object is to kick, hit or throw a ball as
far as possible, it is important that it is struck or hit
with the most velocity. For example is golf, to hit
the ball as far as possible when driving off the tee,
the club head speed must be at a maximum at the
point where it connects with the ball.
Impulse is a product of a force and the time
period over which it is applied, which is equal
to the change in momentum of an object.
Impulse is equal to the force applied multiplied
by the time of the force application:
Impulse = Force x time
Impact is the collision between to objects. Such as in football, when
one person goes for a tackle he must impact on the other person.
Or the impact between the football and another contact surface,
e.g. Ground or persons foot. The types of collision that occurs
determines the motion of the ball after impact. E.g. If the football
hits the side of your foot instead of towards the middle area it will
go off more to the side.
The coefficient of restitution is the measure of
elasticity of bodies involved in a collision. It
looks at the relationship between the velocities
of the objects before the impact compared to
their velocities after the impact. An object may
have a coefficient of restitution between 0 – 1.
When the coefficient of restitution is at 0 the
ball will stick to the floor when dropped. And a
coefficient of 1 means the ball will rebound to
the same height it was dropped from.
All surfaces affect the way a ball will rebound
when dropped onto it. Tennis for example is
played on all different types of courts such as
clay, grass and hard courts. The grass courts
have little friction therefore the ball rebounds
quickly but the clay courts slow down the ball
considerably. The amount of friction between
ball and surface affects the energy loss and
,consequently, the rebound velocity.
Increasing the temperature of a ball increases its
ability to rebound. Increased temperature
causes the air inside the ball to expand, which
increases the ball’s elasticity causing it to
bounce higher. A colder ball will have less
bounce then a ball heated up and has the
opposite affect to the heated up ball.
The coefficient of restitution is increased when the
impact velocity is increased. In such sports like
baseball or tennis the ball comes at high
velocities and the bat or racquet is also moving
in high velocity. These two factors increase the
coefficient of restitution between the bat or
racquet and the ball, and its contributes to a
greater rebound velocity from hitting
implement.
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