BALANCE

When 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 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

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)

# 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

# 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 :

# 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

# When an object is moving but not accelerating it is in dynamic equilibrium.

1/ 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 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

 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/

 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?

1/ 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?