Biomechanics The study of cause and effect FORM 6 PED

Why study Biomechanics? To understand how people can move. 1. To enhance skill performance elite athletes physical challenges

Why study Biomechanics? 2. To lower the risk for injury Exercise equipment & technique shoes & surfaces braces & orthotics Automobiles collisions

Why study Biomechanics? Can a cow really jump over the moon?

Define a Force

Forces and Levers A force is a push or pull. When a force acts upon a body (object) it can produce 3 types of movement. Translation – Moves from A to B. e.g. A golf shot starts on the tee and finishes on the fairway.

Rotation – If force not applied through the centre of gravity the object will rotate e.g. putting spin on a volleyball serve.

Deformation – The object loses shape on impact e. g Deformation – The object loses shape on impact e.g. a squash ball being hit

The main force acting on all parts of the body is gravity. Centre of gravity (COG) can therefore be defined as the point at which all parts of the body are in balance. In men, the COG is about 57% of standing height, in women 55%. Women have more mass concentrated around the hips and below and this gives them an advantage in balance related activities.

These are known as the AXIS OF ROTATION When we produce rotation as a consequence of a force being applied, the body rotates about the COG. These are known as the AXIS OF ROTATION

The body rotates around three different axes. Longitudinal E.g. Pirouette in dance, twist in diving, spinning in ice skating

2. Transverse e.g. forward / backward roll/ somersault

3. Sagital e.g. cartwheel, cricket delivery,

Levers A lever is basically a rigid structure, hinged at some part and to which forces are applied at two other points. Levers consists of three parts. Resistance Effort Falcrum or pivot The point of support, or axis, about which a lever may be made to rotate

FUNCTIONS OF A LEVER Levers perform two main functions: To increase the resistance that can be moved with a given effort, eg. Crowbar. To increase the velocity at which an object will move with a given force, eg. Golf club There are three classes of lever.

Levers-First Class In a first class lever the fulcrum is in the middle and the load and effort is on either side Think of a see-saw

Levers-Second Class In a second class lever the fulcrum is at the end, with the load in the middle Think of a wheelbarrow

Levers-Third Class In a third class lever the fulcrum is again at the end, but the effort is in the middle Think of a pair of tweezers

Newton’s Laws of Motion Sir Isaac Newton (1642-1727) developed 3 laws to explain relationship between the forces acting on a body and the motion of a body.

Law 1 “An object at rest tends to remain at rest unless acted upon by some external force” This is known as Inertia. High level of inertia can be advantageous and disadvantageous in different sports.

Law 2 “When a force acts upon a mass, the result is acceleration of that mass” The greater the force, the greater the acceleration The smaller the mass, the greater the acceleration The mass will accelerate in the direction the force is applied Force = mass x acceleration (F=MA)

Law 3 “For every action, there is an equal and opposite reaction” These 2 forces always work in pairs action force reaction force

The big question.. Analysing the Overhead Serve in Volleyball Try analysing the volleyball serve. Ask yourself “ How is the biomechanical principle – Newton’s Laws of Motion being applied to the overhead serve in volleyball? Where can I see this being applied? This will help you to explain how they contribute to the performance of the serve.

Principles of Balance and Stability What is Stability?

Stability Stability is defined as the ability to hold or maintain a position in space.

Stability The two main elements in maintaining stability are: The position of the COG with respect to the base of support. The direction of the forces involved.

Principle 1 The closer the line of gravity is to the centre of the base of support, the greater the probability of maintaining balance.

Principle 2 The broader the base of support, the greater the probability of maintaining balance.

Principle 3 The probability of maintaining balance is increased when the COG is lowered in relation to the base of support.

Principle 4 The further the body part moves away from the line of gravity, the probability of maintaining balance decreases unless another body part moves to compensate for it.

Types of Motion There are 4 main types of motion;

A) Linear Motion When parts of the body move in straight parallel lines. Quite rare in sporting situations. e.g. tobogganing down a hill, dropping a ball, sliding into first base

B) Curvilinear Motion When points in the body move in curved parallel lines. e.g. free fall skydiving, path of an arrow If the path of two points on a body follow straight parallel lines, the motion is linear. If the path is curved, the motion is curvilinear.

C) Angular Motion Rotation about an axis that can be internal (axis inside the body) or external (axis outside the body). E.g. swinging on a high bar, a forward roll, hammer throwing, pole vault over bar, softball pitch, fosbury flop.

D) General Motion Linear motion of the body as a result of angular motion of other parts of the body. e.g. cycling, swimming, using a wheelchair

Torque ? Torque is a turning force. Eccentric force produces spin. It depends on how far the mass is from the axis and the size of the mass. How do we produce topspin or backspin ? Where do we hit the ball ? How can we generate more spin ?

Momentum Momentum is moving inertia. We can rewrite Newton’s 1st law to include momentum. “An object that is moving will continue to move in the direction the force was applied until another force is applied” The greater the momentum the greater the force required to stop it e.g. small /large snowball. Momentum (kgms) = mass (kg) x velocity (ms)

Momentum can act when an object is translating. This is linear momentum. Momentum can act on an object when it is rotating. This is angular momentum.

Conservation of Momentum When objects collide, momentum is conserved throughout. Momentum before impact = momentum after impact. MOMENTUM = MASS X VELOCITY kgms kg ms

Use the information on Conservation of Momentum and steps below to calculate the speed of the golf ball after impact. A golfer swings a 0.35kg club at 30m/s to hit a 0.004kg golf ball off the tee. After impact his club speed drops to 25m/s. Remember Momentum before impact = Momentum after impact. (M = m x v) Club Momentum Ball Momentum Total Momentum Before Impact After Impact

What is the Ball Velocity? Momentum = mass x velocity Velocity = momentum mass

Use the information on Conservation of Momentum and steps below to calculate the speed of the hockey stick after impact. A ice hockey player uses their stick to strike a 500 gram (0.5kg) puck moving at 2m/s toward their opponent’s goal. The stick has a mass of 2kg and possesses stick head velocity of 25m/s before impact. After impact, the stick head velocity decreases to 17m/s. Remember Momentum before impact = Momentum after impact. (M = m x v) Stick Momentum Puck Momentum Total Momentum Before Impact After Impact