BIOMECHANICS

Achievement Standard 2.2

BiomechanicsDefinition – the study of the body in motion and, in particular, the forces that act on a body and the effects those forces produce.Biomechanics is the study of cause and effect. It examines the internal and external forces on the body and the effects they produce.The force is the basis for all movement.

Newton’s Laws of MotionLaw 1: A body continues in its state of rest or uniform motion unless an unbalanced force acts upon it.An object at rest tends to remain at rest unless acted upon by some external force.For a body to get moving the force has to be greater than inertia acting upon it (inertia = bodies tendency to remain at rest. Greater the mass of the body = greater the inertia). Sherriff pg83.

Newton’s 1st Law illustrated.

Newton’s LawsLaw 2: The acceleration of an object is directly proportional to the force causing it, is in the same direction as the force, and is inversely proportional to the mass of the object.When a force acts upon a mass, the result is acceleration of that mass.

Newton’s LawsLaw 3: Whenever a force is applied there is an equal and opposite reaction.When a force acts upon a mass, the result is acceleration of that mass.

FORCE SUMMATIONTo give an object momentum in activities such as throwing, kicking, or striking an object, the amount of momentum given to the object is determined by ‘the sum of all forces generated by each body part’.To gain maximum momentum, the force needs to be generated by:– Using as many segments of the body as

possible.

Force Summation Cont.– In the correct sequence, using large muscles

first and then the smallest muscles last but fastest.

– With the correct timing.– Through the greatest range of motion.

PROJECTILE MOTIONAs soon as a body becomes airborne it is a projectile.3 factors influence a projectiles flight path:– SPEED: the speed at which the projectile

is released– ANGLE: the angle at which the projectile

was released (optimum angle 45 degrees)

– HEIGHT: height of release can influence horizontal distance covered.

Projectile Jet PlanesMake a paper jet plane.When throwing jet plane, manipulate projectile variables to achieve maximum distance.E.g. throw from different heights – standing, on your knees, on a chair.Use fast and slow hand speeds.Try different angles of release.

Questions

Write a paragraph/sentences explaining how the application of force summation can influence the distance you throw a tennis ball.Explain using Newton’s 1st Law, why a person weighing 60kg would lose a sumo wrestling fight against a 100kg person (mention inertia).

QuestionsRank the following in order of their mass from lowest to highest:– Softball Ping-pong ball– Basketball Shot – Hockey ballWhich of the above balls would have the greatest

amount of inertia?

If you were applying force to overcome inertia it would be:– Greater for the softball or the basketball?– Less for the ping-pong ball or the shot?– Greater for the hockey ball or shot?– Less for the softball or hockey ball?

LEVERSA lever is used when you want to apply more force. Most levers have three clearly identified parts:

1. The fulcrum – the pivot point around which the movement happens. In body levers this is usually the joint.

2. The load – the weight that needs to be moved (resistance).

3. The force – the place where force is applied. In the body this is the effort produced by the muscles contracting.

Levers

Can you think of any household tools/machinery that act as levers?

Function of a Lever2 main functions:To increase the resistance that can be moved with a given effort e.g. crow bar.To increase the velocity at which an object will move with a given force.There are three classes of lever:– First class– Second class– Third classThe human body consists mainly of third class

levers. Third class levers generate speed rather than force. We can increase the velocity at which an object can move with a given effort. V = M / S

Levers in Sport

In some sports the equipment you use acts as an extension of the levers in your body and helps to generate greater force or speed.Give some examples of levers in sport.Longer levers result in more speed, beneficial for striking and throwing objects.Shorter levers result in greater strength, beneficial for pushing, pulling, and lifting objects.

QuestionsJohnny needs some help with his tennis serve. He has a low success rate with not many serves making it over the net.You need to come up with 3 coaching pointers using Biomechanical Principles and Functional Anatomy that will help improve the success of Johnny’s serve.

CENTRE OF GRAVITYThe point at which all parts of an object are equally balanced.Standing up right our centre of gravity is around our navel.The centre of gravity changes depending upon what position the body is in.The centre of gravity can lie outside an object.Generally, the lower the COG the more stable an object will be.

LINE OF GRAVITY

The vertical line that passes through the centre of gravity to the ground.The line of gravity is important when determining the stability of an object.If the line of gravity falls within an object’s base of support the object is relatively stable (and vice versa).

BASE OF SUPPORT

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.

QUESTIONSCopy each of the objects and draw in the centre of gravity.Which player is more stable? Explain using the words base of support, line of gravity and COG.

MOTIONLinear motion – is in a straight (vertical) line. All parts of the body move in the same direction and at the same speed. [Give examples]Angular motion – occurs around an axis. This can be internal (body parts rotating around a joint) or external e.g. ………..General motion – a combination of linear and angular. This is the most common of all movements, as most human movement requires rotation of body parts around joints e.g. ……….