kinetic concepts

• Mass is the amount of matter an object is made up of, it is measured in kilograms (kg)
• Inertia describes a body's resistance to change in its state of motion
• There is a direct relationship between the amount of mass to the object's inertia.

  Eg. To improve take off speed improve your ability to generate force by increasing muscle mass in the legs.
• A force can...

  • be a push or pull (muscle pulling on the bone)
  • change the shape of an object (stretch, squash, or twist)
  • move an object (speed it up or slow it down)
  • sometimes not be obvious (eg. gravity or when you run and push against the earth)
• Force (F) = mass (m) x acceleration (A)
• If you want to apply more force, get bigger (mass) and/or faster
• Types of friction:

  • friction
  • air and water resistance
  • gravitational force
  • weight
• Friction occurs when two surfaces come into contact with each other. Friction opposes the motion of an object
• There are times in sport when friction needs to be decreased OR increased to enhance performance
• To start an object moving across a surface, you must overcome the friction by applying an increasingly greater force
• Eg of increasing friction to enhance performance


  Footy boots to create friction wile running, gymnast using chalk on their hands to increase friction between hands and the bar.
• Eg of decreasing friction to enhance performance


  Oil on AFL players shoulders to avoid tackles, hard smooth skis for downhill skiers
• When an object moves through air or water it will experience drag force. Drag force opposes the direction of movement slowing it down
• Drag is effected by factors such as...

  • air density
  • cross sectional area of the body
  • speed the object is travelling
• On earth, gravitational force is the force that causes objects to fall downwards. The acceleration due to gravity is 9.8m/s
• Weight refers to the force that is exerted on the body or an object by gravity. Weight is directly proportional to the mass of an object
• Weight (W) = mass (m) x gravity (G)
• Momentum describes the quantity of motion a particular body of mass has
• Momentum (M) = mass (m) x velocity (v)
• An object can only have momentum if it is moving. The greater its momentum, the further it may travel and the harder it is to slow or stop the object.
• Summation of momentum is where body parts move in a sequence to produce a desired (maximal) amount of force
• To achieve summation of momentum, athletes spend hours rehearsing their skills to improve the timing and sequence of their movements to ensure the desired quantity of force is generated
• Eg of summation of momentum in sport...


  Cricket bowl, tennis serve, basketball lay up
• The first principle to maximise summation of momentum is to activate the STRONGER and LARGER muscles first.
• The second principle to maximise summation of momentum is using as many body parts as possible, enabling force to be generated over a greater time.
• The third principle to maximise summation of momentum is to transfer from one body part to another when at maximal velocity.
• The fourth principle to maximise summation of momentum is to have a stable base to enable an efficient acceleration of body parts
• The fifth principle to maximise summation of momentum is to ensure appropriate follow through to prevent negative acceleration of body parts
• Conservation of momentum refers to when two bodies collide, the combined momentum of the two bodies is conserved (stays the same)
• A sporting example of conservation of momentum is a bowling ball transferring momentum to a pin, but the combined momentum of the ball and pin is the same when added up.
• Impulse is equal to the change of momentum in an object.
• Impulse = force x time
• Greater change in momentum (impulse) can be achieved when a force is applied for longer time and a greater force is applied.
• A sporting example of increasing impulse is loosening the strings on a tennis racket to increase contact time, resulting in greater impulse and momentum.
• Angular momentum is the rotation of an object around an axis.
• Angular momentum = moment of inertia x radius^2
• Moment of Inertia of a body is its tendency to resist changes in rotary motion.
• Conservation of angular momentum refers to when a body is in flight the angular momentum is conserved and cannot change.
• A sporting example of conservation of angular momentum is as the gymnast moves into the tuck position, the moment of inertia decreases and angular velocity increases, but the angular momentum remains constant
• Newtons 1st law of motion (the law of inertia)


  An object whether at rest or in motion will continue in that state unless acted upon by an external force.

  AKA. objects will not move from their state of being unless forces acting on them become unbalanced