 # By Cade and Georgia.  Newton’s laws of motion, including an understanding of force, mass and weight, acceleration and inertia applied to sport and physical.

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By Cade and Georgia

 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 radius 2

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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