Balance & StabilityIntroduction to Biomechanics - 1

Lorna McAvoy - AJHS PE Dept

What is Biomechanics?

Lorna McAvoy - AJHS PE Dept

Analysing the performance of skills is an important task for coaches and athletes. It allows them to correct poor technique and improve in their future performance.This analysis of skills and performance is known as BIOMECHANICS. It includes understanding concepts such as:• Stability• Motion (Projectile, Linear etc)• Newton's 3 Laws• Levers• How gravity effects objects• Summation of Forces• Impact and ReboundIn this unit we will learn about Summation of Forces, Principles of Stability and Levers.

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

There are two forms of balance:

1. Static – when a balance is held in a position2. Dynamic – is balancing when moving

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

Video

Gymnastics - Beam

Lorna McAvoy - AJHS PE Dept

Question?

What position do you think is the most stable?

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

Gravity

Lorna McAvoy - AJHS PE Dept

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 speedWhen 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

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

Centre of gravity

Centre of Gravity

Line of Gravity

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

Line of gravity

Centre of gravity

Requirements for Balance

Centre of GravityPoint at which all of the body parts are equally balancedBase of SupportArea within the bodies contact with the ground

Line of GravityLine that passes vertically through the centre of gravity

Lorna McAvoy - AJHS PE Dept

Who is more balanced? Why?

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 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 or body is.

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

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

Class Task

Number of Contact Points

Sporting Example 1 Sporting Example 2

1 In Ice Skating, I performed an arabesque. My point of contact was my right foot.

234 In Athletics I started my

100m race with a crouch start. My points of contact were my feet and hands.

Lorna McAvoy - AJHS PE Dept

Different sports require you to use different of bases of support with a variety of points of contact. Copy and complete the table giving examples of the

sports and your base.

Class Task 1 (Picture Board)

•Collect a picture sheet from Miss McAvoy

•Stick in your book

•Label the centre of gravity, line of gravity and base of support in eachLorna McAvoy - AJHS PE Dept

Extension Task (Practical)Place a 40cm object such as a drink bottle or cardboard box on the ground.

No part of your body, except your feet are allowed to touch the ground.

Your aim is to pick the object up with your mouth.

Discuss the role stability and balance played in allowing you to do this task. Identify what occurred to your centre of gravity, line of gravity and base of support in order to achieve this task.

Lorna McAvoy - AJHS PE Dept