BIOMECHANICSBiomechanics is the study of

the internal and external forces which act on the body, and the effects produced by

those forces.

• Biomechanics is a very useful science in the study of human performance especially in the area of perfecting technique.

• Biomechanics forces may be either • a) static – which is concerned with bodies

at rest, or• b) dynamic – which is concerned with

forces producing movement

MOTION• TRANSLATORY – this is when all parts of the body

follow parallel lines. There are two types:• Linear – all parts of the body move in straight

parallel lines• Curvilinear – all parts of the body move in curved

parallel lines.• ANGULAR, or ROTARY – This when a body moves

about an axis. There are two types:• Internal Axis – the axis is within the body• External Axis – the whole body travels around an

axis that is outside the body

GENERAL MOTION• Most motion is in fact a

combination of both angular and linear and we describe this as GENERAL motion.

• For example a cyclist has angular motion with the wheels, the pedals, and his limbs, but the bike frame and his trunk experiences linear motion.

What is a projectile?

Any body released into the air is a projectile. This means that once it is in the air it has no extra propulsion. A body can be released into the air by either –

Throwing – eg. Discus,

Striking – eg. tennis

Projecting the body itself – eg. High jump

PROJECTILE MOTION

The TRAJECTORY (path of a projectile) is influenced by two sets of factors Propelling factors

(ie factors at its release)

Speed of release Height of release Angle of release

Factors in the air Gravity Air resistance Spin Aerodynamics

Effects of Air Resistance and Aerodynamics

A - No air Resistance

B – Air resistance

http://www.walter-fendt.de/ph11e/projectile.htm We can draw some conclusions Speed of release - The greater the speed of

release, the greater the horizontal distance Height of release – the greater the height of

release, the greater the horizontal distance Angle of release – There is an optimum angle

of release for each object, but that will depend on a number of factors including aerodynamics of the object and height of release eg. In Volleyball, what advantage is there in a jump serve?

What happens when we have different angle of release?

Angle of releaselook at the requirementsfor different activities Activity Tennis Serve Volleyball float serve Long jump Discus High jump Standing back

somersault

Angle (degrees) -3 to 15 13 to 20 17 to 22 35 to 39 40 to 50 75

What are the different objectives for our projectiles? And, what do we need to do to maximise our chances of success?

Height eg high jump, pole vault Maximum possible speed of release Maximum possible angle of release Distance eg discus, long jump Maximum possible speed of release Correct angle of release for activity Application of spin in some cases Speed eg rugby pass Maximum possible speed of release Lowest possible angle of release Accuracy eg archery, netball

LEVERS

Biomechanics and Levers• A lever is a mechanism made up of a lever arm (with 2

forces acting on it) and a pivot point. It has three parts • The Fulcrum or Pivot point - The point about which

the lever works • Load or Resistance - The force being overcome by

the lever system • Effort or Force - The force being applied to overcome

the load • There are three classes of levers -• 1. First class - See-saw and Crowbar• 2. Second class - Wheelbarrow• 3. Third class - The boom of a crane

1st Class Lever

The fulcrum lies between the effort and the load

2nd Class Levers The fulcrum

lies at one end of the lever arm with the Effort being applied at the other end

3rd Class Lever The fulcrum

lies at one end of the lever arm with the effort being applied between it and the load

3 classes of levers

INERTIA• Inertia is a bodies resistance to change in

motion.• Inertia is described in Newton’s First Law • “A body continues in it’s state of motion or rest

unless acted on by a force”• Inertia is related to mass well as shape and

friction• http://www.physicsclassroom.com/Class/newtla

ws/U2L1b.html

Inertia in Action

• Inertia is easily observed if you think about being in a vehicle. When it brakes hard, you are thrown forward. This is because you have your own moving inertia. When the vehicle alters its own inertia you still continue with yours until a force works on you

NEWTON’S THIRD LAW• http://www.physicsclassroom.com/Class/newtla

ws/U2L4b.html• Newton’s 3rd law relates to Action / Reaction• “For each and every action, there is an equal

and opposite reaction”

FORCE SUMMATION• The velocity of

a projectile depends on the speed of the last part of the body at the time of contact or release

FORCE SUMMATION• If you wish to achieve

maximum velocity, it is important that each body part is used in the correct sequence.

• You use the strongest, heaviest muscles first, before using the smaller, faster muscles last.

• This overcomes inertia

TIMING• The timing of the application

of the forces is vital• A body part should begin to

move when the previous body part is exerting maximum force / speed

• Eg. In a well-timed Volleyball spike; the forearm begins to extend at the elbow just as the upper arm begins to deccelerate