CQ3 – How do biomechanical principles influence movement? PRELIMINARY HSC PDHPE CQ3 – How do biomechanical principles influence movement?

How do biomechanical principles influence movement? Students learn about: motion the application of linear motion, velocity, speed, acceleration, momentum in movement and performance contexts Students learn to: apply principles of motion to enhance performance through participation in practical workshops balance and stability centre of gravity line of gravity base of support apply principles of balance and stability to enhance performance through participation in practical workshops fluid mechanics flotation, centre of buoyancy fluid resistance   apply principles of fluid mechanics to enhance performance through participation in practical workshops describe how principles of fluid mechanics have influenced changes in movement and performance, eg technique modification, clothing/suits, equipment/apparatus force how the body applies force how the body absorbs force applying force to an object. apply principles of force to enhance performance through participation in practical workshops.

Balance and stability The concepts of stability and balance are closely related to equilibrium. Stability is concerned with the resistance of a body to changes in its equilibrium; that is, changes in its linear or angular acceleration. When an individual can assume a stable position and then control that position, he or she is said to be in a state of balance. There are two types of balance: • If the body is at rest (not moving) it has static balance. • If the body is moving, it has dynamic balance.

centre of gravity All masses within the gravitational field of the earth experience an attraction towards the centre of the earth. The greater the mass, the stronger the attraction. The gravitational force that the earth exerts on objects is their weight, which is the product of the mass of the object, the mass of the earth, and acceleration due to gravity (9.8 m/s2). If the whole force were to be concentrated at a single point, this would be the centre of gravity. The centre of gravity (CG) is also the balance point of the system or the point at which all mass seems to be concentrated. Remember:

line of gravity A straight line drawn from the CG to the ground is called the line of gravity. Individual body segments (limbs) also have their own CG. An object is most stable when the line of gravity falls through the centre of the base of support. Increasing the area of the base of support will generally increase stability. Remember: a body may be stable in one direction but not in another.

base of support The base of support of a body is the region bounded by the body parts in contact with a surface that is applying a reactive force against the applied force of the body. For example, when you stand up, the area covered by your feet is your base of support. If you hang from a parallel bar, your base of support is the area between the outer limits of your hands. Any other objects or surfaces that exert a force against your body in some direction other than vertical also form part of your base of support. The greater the mass of an object, the greater its stability. It takes a greater force to move a heavier object. Wrestling and boxing competitions, in which stability is an important component, enforce weight divisions to make competition fairer.

Revision/Homework task Answer/complete the following statements/questions: apply principles of balance and stability to enhance performance through participation in the following: 1 In pairs, have one partner try to push the other off balance when in the following positions. Ensure that the push is always from the side.  a standing with arms above the head on tip toes b standing normally c standing with knees bent d standing with feet wide apart to the side e standing with feet wide apart to the front f kneeling on all fours   2 Copy the continuum below and mark on it the degree of stability for each position a to f above. ▲_________________________________________▲_____________________________________________▲   Most stable Least stable

Revision/Homework task Answer/complete the following statements/questions: 3 Describe two activities in which the athlete wishes to increase stability in order to improve performance. 4 Describe two activities in which the athlete wishes to decrease stability in order to improve performance. 5 Analyse the techniques employed by a gymnast or diver to maintain stability when executing a handstand.