Chapter 9: Monentum, Angular Momrmtum And Levers

Question 1

• What is force and give an example.
• What are Newton’s 3 laws?
• What is momentum?
• What is the conservation of momentum
• Use the transfer of momentum in a snooker situation.
• Using the theory of momentum, explain what happens when a tennis racket hits a moving tennis ball.
• Define impulse
• Explain the application of impulse in hockey
• Using the idea of impulse, how can an object decrease the force applied to it by another object, given a set force. Provide a sporting example.

Answer 1

• A pushing or pulling action that changes a body’s state of motion. Eg a shot put can be moved when another body exerts a force on it.
• Law of inertia, Law of acceleration and Law of opposite reactions.
• Amount of motion possessed by a moving body expressed as p=mv
• A moving object has momentum. Unless a force is applied to the object to increase or decrease its speed, the momentum is conserved.
• When a cue ball in snooker is hit into another ball, the 2nd ball moves at the same speed, direction and momentum as the first due to the transfer of momentum.
• The racket has a much greater mass than the ball so after making contact, the transfer of momentum means the ball gains speed and direction in a manner controlled by the player holding the racket.
• Change in momentum which is expressed as Impulse=F x t
• A hockey player who drags the ball can keep the ball on the stick for the longest possible time to increase the force and therefore maximise the ball’s impulse.
• By increasing the time of the collision of two objects. F=Impulse/t. Eg in boxing if you anticipate and ride the punch, relaxing his neck, it increases impact time hence decrease the force.

Question 2

• Define elasticity
• define coefficient of restitution
• Define moment of inertia
• Using the theory of moment of inertia, explain how a figure skater can spin faster.
• Explain how a tennis player can change their moment of inertia.
• Define angular momentum
• What are levers are their purposes.
• What are first class levers?
• What are second class levers?
• What are third class levers?
• What is the force?
• What is the resistance arm?

Answer 2

• Degree of compression then expansion to the original shape.
• The bounciness of a implement measured by: height of rebound / height of drop.
• The resistance to rotational motion.
• They can move their arms from outstretched to closer to the body. This will bring the object’s mass closer to the axis of rotation to reduce the moment of inertia to spin faster.
• Adjusting the radius of rotation by adjusting the grip moving hand up and down handle and change the mass of the racket.
• Quantity of angular motion possessed by a body
• Bar-like objects that turn about a fixed point and to which forces are applied at two other points. They allow us to apply increased forces and to generate greater speed.
• Levers with the fulcrum between the load and force.
• Levers with the load between the force and fulcrum.
• Levers with the force between the load and fulcrum.
• Distance from point of force to fulcrum.
• Distance from point of load to fulcrum.

Question 3

• What is the advantage of having a longer force arm?
• What is the advantage of having a longer load arm?
• Is velocity greater at the end of a long or short lever? Use a sporting example.
• Give a sporting example where a combination of short and long levers is used.
• What is torque / moment?
• What factors must a hammer thrower aim to combine to be successful?
• What is inertia?
• When moment of inertia is high, is angular velocity high or low?

Answer 3

• Less effort required to move a resistance.
• Increases velocity of the system/implement
• Long lever, eg tennis player serve is hit at the highest height for more velocity.
• During a soccer kick, the leg begins to forward swing with the knee flexed (short lever) for greater acceleration. The leg is straightened before contact increasing lever length and therefore the velocity if the foot.
• The measure of the turning effect of a couple
• Combine a powerful body (to generate force) with long levers (to generate speed) and fast rotation about an axis (to generate torque).
• Degree of difficulty in making a stationary object move, or making a moving object stop.
• Low