Joint Movement Agonist Antagonist

Elbow

Shoulder

Trunk

Knee

1 2

Balance and Stability

Gravity

What is gravity?

It is a force that pulls all objects towards the ground. It stops us flying off into space

It is applied constantly, it pulls everything towards the centre of the earth at the same speed

When a ball is thrown up into the air, gravity is the force acting to pull it back down to the ground

Centre of Gravity

The centre of gravity is the point located on an object where the mass is evenly distributed

For symmetrical objects like a ball the centre of gravity is the actual centre

Centre of gravity

Centre of gravity

COG - HumansFor irregular objects that can change their shape the centre of gravity is always changing. Eg. Humans

For normal human beings standing upright, their centre of gravity lies around the area of their navel.

This can change depending on what position the body is in eg when a person is doing a bridge

Centre of gravity

Line of Gravity

Is the vertical line that passes through the centre of gravity to the ground

Base of support

Line of gravity

Centre of gravity

Base of supportIs the area within an object’s point of contact with the ground.

The larger the area the base of support covers, the more stable an object will be.

Base of support Base of support

Balance

An object is balanced when forces acting on it are equal – this referred to as stable

There are two forms of balance:

Static – when a balance is held in a position

Dynamic – is balancing when moving

Anything can be balanced if its centre of gravity is directly over its base.

How do these people remain balanced?

Principles of BalanceBalance is a desirable attribute in the performance of many skills.A body is most stable when the 3 principles of balance are applied

1 Anything can be balanced if its centre of gravity is directly over its base of support

2 The wider the base of support the more balanced or stable the object of body is.

3 The lower the centre of gravity the more balanced or stable the object is.

As one body part moves another must move to compensate that movement

2. Explain how the shooter in the image could make herself more stable while shooting.

(Refer to the principles of balance to help you)

1. Explain why it is important to be stable when shooting in netball.

Applying knowledge (assessment)

3. Justify your answer in Q2 by stating how and why you think this will help improve performance.