Newton’s Laws

Objectives To understand how Newton’s Laws of Motion relate to Olympic sports. To show how Newton’s laws can explain the outcomes in Olympic sports.

Newton’s First Law (Law of inertia) An object will continue in a state of rest or uniform motion unless acted upon by an external force. If an unbalanced force acts on an object, it will accelerate in the direction of the unbalanced force. If an object is given a certain initial velocity and there are no unbalanced forces acting on it, the object will continue along its original path in a straight line.

Newton’s Second Law (Law of acceleration) When a force acts on an object, the object is accelerated by an amount directly proportional to the force applied and inversely proportional to the mass of the object (F = ma). The greater the force being exerted on an object, the faster the object moves.   The greater the mass of the object, the slower the object will move in relation to a lighter object with the same force applied.    A big mass (tennis ball) is harder to accelerate than a smaller mass (table tennis ball).

Newton’s Second Law Every object that is in motion has a certain mass and a certain velocity. The product of these two values is known as it’s momentum This is the ‘quantity of motion that a body possesses’. Momentum= Mass x Velocity If two objects are travelling with the same velocity the one with the greater mass has the greater motion and vice versa.    Jonah Lomu had a greater mass than Jason Robinson, therfore greater momentum

Newton’s Second Law - Hockey If a player strikes the ball, its acceleration is determined by the mass of the ball and how hard the player hits it (F = ma). If the ball were heavier (larger mass), it would accelerate less. If the player hits the ball harder (larger force), the ball accelerates more quickly.

Newton’s Third Law (Law of action/reaction) For every action there is an equal and opposite reaction When a sprinter exerts a force on the blocks there is an equal, but opposite, force exerted back on the sprinter which drives him forward. But as the blocks are attached to the earth they have a greater mass which results in a greater force being applied to the sprinter. This is know as the ground reaction force. Similarly a footballer applies an action force to the ball, and receives an equal and opposite reaction force which he can feel on his foot. Question: When hitting a baseball, if we call the force on the bat against the ball the action force, what is the reaction force?

The reaction force is the force exerted by the ball on the bat. Newton’s Third Law When a swimmer turns, the pool wall pushes against the swimmer with the same force as the swimmer pushes against the pool wall. When a weightlifter pushes against the ground, the ground pushes against the weightlifter with the same force. When a tennis player hits a ball with their racquet, the tennis ball exerts an equal but opposite force on the player’s racquet. Can you think of any more examples? Answer: The reaction force is the force exerted by the ball on the bat.

Questions Q1. As a baseball flies through the air, it slows down. According to Newton’s First Law, this can’t happen unless some force acts on the ball. Where does this force come from? Q2. Why, given Newton’s Second Law, can you throw a baseball much farther than you can throw a shuttlecock? Q3. Give an example of Newton’s Third Law from the following Olympic sports: diving, volleyball, fencing, athletics and archery.

Plenary Homework You will be given one of three sporting scenarios; 1. Sprinting (from start to finish) 2. High Jump (from start to finish) 3. Kicking a ball (including moving towards the ball) For your designated scenario go into as much detail as possible as to how all of Newton’s Laws relate to the execution of these movements.