UNIT 1 – AREA OF STUDY 2BIOMECHANICAL MOVEMENT

PRINCIPLES

BALANCE

EQUILIBRIUMWhen we talk about an object being in a state of equilibrium, it means being more than stable or balanced.

Balance is important in many sporting activities.

Can you name 3 sporting activities where balance is important?

To understand equilibrium we must first have a solid understanding of TORQUE.

TORQUE• Torque is the effect caused by the application of an

eccentric force. Torque is equal to the product of the force being applied and the lever arm

• LEVER ARM – The shortest perpendicular distance between the line of force and the axis of rotation.

• Torque = force x perpendicular distance

TORQUE• The lever arm is the perpendicular distance from the axis

of rotation to the force’s line of action (see below). In the elbow joint, the torque gets smaller as the joint angle increases or decreases from 90 degrees because the perpendicular distance from the line of force to the axis decreases (lever arm)

FORCE COUPLE# Often there are 2 forces acting on an object

# When these forces are equal in size but opposite in direction, they create a force couple.

# A force couple produces torque in the same direction and the object will rotate about the axis of rotation

EQUILIBRIUM CONTINUED# An object is in equilibrium when there are no

unbalanced forces or torques acting on it# It is neither motionless or moving, that means it

is not accelerating.# In a nutshell equilibrium is when all forces and

torques are balanced

# There are 2 types of equilibrium :

STATIC EQUILIBRIUM# When an object is in static equilibrium it is

totally motionless but it must fit 3 criteria:

1/ The sum of all the vertical forces acting on the body must be zero

2/ The sum of the horizontal forces acting on the body must be zero

3/ The sum of all torques must be zero

DYNAMIC EQUILIBRIUM# When an object is moving but not

accelerating it is in dynamic equilibrium.

QUICKFIRE QUESTIONS1/ Explain 2 ways in which torque can be reduced.

Provide a practical application to support your answer.

2/ Draw a labeled diagram to demonstrate a force couple in a sporting situation.

3/ Define static equilibrium. Give 2 examples of an athlete in a state of equilibrium in different sporting situations.

4/ A junior shot-putter holding the shot at their neck is in equilibrium just prior to beginning their action to release. Describe how the conditions of equilibrium can be changed to release the shot.

STABILITY AND BALANCE

Stability is the ability of a body to resist a change in its current state of equilibrium.

Balance is the state of equilibrium and the ability to control it.

In some sports the aim is to increase stability and in others it is beneficial to decrease stability

Wrestlers use positions that increase their bodies’ stability, making it more difficult for their opponents to disrupt their equilibrium

WRESTLING AND BALANCE

WHEN DO SPORTS NEED BALANCE? Can you name 3 sports that rely

heavily on balance and explain how these sports people are able to improve their balance.

1/

2/

3/

FACTORS AFFECTING STABILITY

A body’s ability to maintain equilibrium is affected by:

BODY MASS

FRICTION

BASE OF SUPPORT

POSITION OF CENTRE OF GRAVITY

Can you explain how these could affect stability?

INVESTIGATING STABILITY

QUICKFIRE QUESTIONS1/ Define equilibrium, balance and stability.2/ List 4 sporting examples where contact

surfaces are manipulated to either increase or decrease the stability of an athlete.

3/ List the 4 factors that can affect stability. Explain the effect each has on the stability of an object.

4/ Coaches often ask junior athletes to ‘Bend your knees’. How would this instruction benefit a young athlete?