1. PHED 3 Exercise Physiology Aerobic Energy System
A2 PE
PHED 3
Exercise Physiology
Aerobic Energy System

2. Newton's Laws

3. Newton’s First Law- The Law of Inertia
Inertia is the reluctance of a body to move or change its state of motion.
Newton's First Law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. It may be seen as a statement about inertia, that objects will remain in their state of motion unless a force acts to change the motion.
e.g. a stationary object has balanced forces acting on it. These forces are gravitational pull and reaction force, they are both of equal magnitude and balance each other out. Until another force acts upon it it will remain still or motionless, the new force applied is the ‘action force’ causing it to overcome inertia and therefore change its state of motion. Once the object moves it will continue to travel with constant velocity in a straight line as long as the forces remain balanced.

4. Newton’s first Law: Inertia (Sporting example)
‘An object will remain stationary or continue to move at the same speed and in a straight line unless an external force acts upon’. Here the ball will continue to move unless and external force either friction from the pitch, air resistance, the back of the net or the goalkeeper acts upon it.

5. Newton’s Second Law- the law of acceleration
This law states that the acceleration of an object is directly proportional to the force acing upon it.
The rate of change of momentum of a body is proportional to the force causing it and takes place in the direction in which the force acts.
Therefore in order to create a greater acceleration greater forces must be generated. Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).

6. Newton’s second law: Acceleration (sporting example)
The ball was stationary with balanced forces acting upon it, The fast striking action has caused the ball to accelerate in the direction of the muscular contraction being applied to it, the shape and light mass of the ball has helped it create a fast acceleration.

7. Newton’s third law- the law of action/reaction
For every action, there is an equal and opposite reaction.
This means that in every interaction there is a pair of forces acting.

8. Newton’s third law: Action/reaction (sporting example)
The force being applied by the golf club is equal to the resistance force being applied by the golf ball. What makes the golf ball move is the muscular contraction adding to the golf club making the forces unbalanced. The golf ball will now accelerate.

9. Past exam Questions-
(b) Use Newton’s three laws of motion to explain how a performer can move towards
the ball in one of these games (hockey, golf, rugby) (4 marks)
(c) In hockey, golf and rugby, the performer may hit or kick the ball into the air, where it becomes a projectile. Explain how the various forces involved act to affect a projectile during its flight.

10. Answer
(b)
1. (First Law) force required to change state of motion (of performance);
2. (Second Law) size of force governs change of momentum; (do not credit
F=MA)
3. Mass remains constant;
4. Force governs the magnitude of the acceleration given to the ball;
5. And direction;
6. (Third Law) equal and opposite (ground) reaction force;
7. Performer applies force to ball through muscle contractions. 4 marks
(c)
Parabolic flight path/trajectory/parabola;
2. Gravity reduces height achieved/brings projectile back to earth;
3. Acts on the vertical component;
4. Air resistance has no negligible effects;
5. Horizontal components of most sports projectiles;
6. Some projectiles affected by air resistance/shape . golf ball dimples 3 marks

11. Key words Weight, Velocity, Mass, Acceleration, Speed, Gravity,
Inertia,
Distance,
Displacement,