1. PHED 3 Exercise Physiology Forces
A2 PE
PHED 3
Exercise Physiology
Forces

2. The role of force in sport…
Forces can cause:
A body to move
A moving body to accelerate
A moving body to decelerate
A moving body to change direction
A body to change shape

3. Types of force…
As an athlete, If you understand the role of force in sport then the you can manipulate techniques to use force to best effect.
There are two different types of force: Vertical force which includes weight and normal reaction and Horizontal force which includes friction and air resistance.

4. Vertical Forces – Weight…
A weight force is equal to the mass of an object or body and the acceleration due to gravity.
Weight = Mass x Acceleration due to gravity
Weight always acts as a downwards, towards the centre of the earth.

5. Vertical Force – Reaction Force…
Reaction forces will always occur whenever two bodies are in contact with each other because every action has an equal and opposite reaction.
Reaction forces will always act
as right angles to the contacted
surface.
E.g. the reaction forces that
might occur on a tennis player
playing a forehand drive.

6. Horizontal Forces – Friction…
Friction is a resistive force encountered when two or more bodies in contact move past one another.
Factors that affect friction include;
the roughness of the surfaces in contact (the rougher the surface, the greater the friction)
the greater the downward force or mass of an object the greater the friction
warmth of surfaces (dependent on the surface the friction will either increase or decrease)

7. Horizontal Force – Air resistance…
Air resistance is the force of air pushing against a moving object. It is a form of fluid friction that acts on something moving through air.
The degree of air resistance experienced depends on;
Velocity – the faster the moving object, more subject to the effect of air resistance
The larger the frontal cross-sectional area, the greater the effects of air resistance
The rougher the surface the more it will affected by air resistance and drag.

8. Free Moving Diagrams
Free Moving Diagrams are used to show the relative magnitude and direction of all the forces that are acting upon an object or body in a given situation. For example, the length of the arrow reflects the magnitude of the force and the position of the arrow head reveals the direction in which the force is acting.

9. How you draw forces onto a sporting movement
When asking you to draw forces onto a sporting movement it is bascially asking you to draw:
Direction of Travel
Air resistance
Weight
Direction of Travel=The direction in which the object/person is moving towards after musculaur contraction
Air resistance= This will be determined by shape of the object, if it is round it will have very small air resistance, if it has parts which will catch the air e.g a shuttle cock then it will have high air resistance
Weight=The weight of an object will also determine how long it stays in the air/how fast an object is.

10. EXAMPLES…
When drawing the forces the size of the arrow has to be relevant to the size of the force acting apon the object
Direction of travel
Air resistance
Weight
Here the shotput has all 3 forces acting apon it. The direction of travel is larger than the air resistance because of the power power being put into theaction and the shape of the object. Mass will be larger than air resistance becasue the putt is heavy

11. EXAMPLES…
Direction of travel
Weight
Air resistance
Because of the shape of the shuttlecock it has a large amount of air resistance
Which will mean it will not go that far in flight in the air. The weight of the cock
However is very light therefore it hit hard it will go a small distance

12. Impulse
Impulse is concerned with the length of time a force is applied to an object or body and relates to a change on momentum that occurs as a consequence. (impulse = force x time)
Impulse can be used in sport to add speed to a body or object and slow down moving bodies slowly on impact.

13. EXAMPLE
The O’Brien technique where a shot putter performs a one and three quarter turn before release is designed to maximise the time over which a force is applied to the shot, increasing out-going acceleration.

14. This graph represents an accelerating body
This graph represents an accelerating body. The shaded area below the graph (- ve impulse) represents a body landing on the ground. The +ve impulse above the graph represents the impulse of a body due to the ground reaction force.

15. On this body diagram add arrows to identify the relevant horizontal and vertical forces in operation.

16. Direction of movement AR
friction
weight