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Biomechanical Definitions Chapter 4

Biomechanical Definitions Chapter 4. FORCE. Force is the “push” or “pull” placed upon an object to: Get it moving Speed it up Slow it down Stop it Change it’s direction. FORCE (continued…). Force is used to change the velocity of something.

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Biomechanical Definitions Chapter 4

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  1. Biomechanical DefinitionsChapter 4

  2. FORCE Force is the “push” or “pull” placed upon an object to: • Get it moving • Speed it up • Slow it down • Stop it • Change it’s direction

  3. FORCE (continued…) Force is used to change the velocity of something. Internally, force is produced by muscle contractions Externally, force is generated by gravity, friction, water and air

  4. FORCE (continued…) Force = Strength or power applied to change the body’s state of motion Examples: • ___________________________ • ___________________________ • ___________________________

  5. INERTIA • Inertia is the tendency of an object to maintain it’s state of motion (velocity), whether it is stationary or moving • The inertia of an object is directly related to it’s mass- (it is harder to move an object made up of more matter!!!)

  6. INERTIA • To alter an object’s motion we must apply an unbalanced force to overcome it’s inertia • The force may alter an object’s speed and/ or direction of movement E.g: A Spike in beach volleyball

  7. Mass is the amount of matter that makes up an object Eg: 1kg of feathers vs 1kg of bricks Weight is the force exerted by the earth’s gravity on an object MASS & WEIGHT

  8. VELOCITY Velocity =distance time • Velocity measures the speed of an object There are 2 main characteristics of velocity: • Speed (how quickly it covers the ground) • Direction

  9. VELOCITY • The unit of measurement we use for velocity is: *Metres per second (m / s) • A stationary object is said to have a velocity of zero • An object travelling 5 metres each second has a velocity of = ____________________________

  10. Momentum is the measure of the amount of motion possessed by a moving body (mass x velocity) The units of measurement we use for momentum are kilograms and metres per second (kg & m/s) MOMENTUM

  11. MOMENTUM The momentum of an object is directly related to it’s mass and it’s velocity

  12. MOMENTUM 1. “If 2 objects of different mass are moving with the same velocity it will be harder to stop the object with the greater mass” Eg: St. Kilda AFL footballers Fraser Gehrig (110kg) vs Stephen Milne (83kg) 2. “If 2 objects of identical mass are moving at different velocities it will be harder to stop the object moving at a greater velocity” Eg: A tennis serve Andy Roddick vs Maria Sharapova

  13. MOMENTUM • When two bodies collide, the one that possesses the most momentum will be least effected Therefore: On a rugby field a smaller, faster moving player knocks over a bigger, slower player. The smaller player has more momentum due to extra speed on the field

  14. Weight = 90kg Velocity = 1.8m/s Weight = 120kg Velocity = 1.2m/s MOMENTUM

  15. MOMENTUM Momentum = MASS x VELOCITY X

  16. IMPULSE • The application of force over a period of time which changes the velocity(speed) of a body or object **The larger the impulse applied, the greater the change in momentum Eg: The spin before a discus is thrown. This technique increases the time over which force is applied

  17. ACCELERATION Acceleration = The rate of change in velocity It is how quickly an object can change velocity when an unbalanced force causes movement. **Newton’s 2nd law of motion explains this principle.

  18. ACCELERATION Two identical shot puts are acted on by an unbalanced force ( they are thrown), • One is thrown by an Olympic athlete • The other is thrown by a Beginner Result: The shot put thrown with greater force (Olympic athlete) will have greater acceleration

  19. ** Acceleration is measured in metres per second squared M / S² “Acceleration is directly affected by force….the greater the force used, the greater the acceleration” More force = More Acceleration ACCELERATION

  20. ACCELERATION • Mass also affects the acceleration of an object. For Example- If the force applied to two balls is the same (a tennis serve), the ball with a smaller mass will have a greater acceleration Vs

  21. ACCELERATION • Acceleration is important at the start of a lot of sporting events, especially sprinting. • Sprint cyclists can accelerate to 16km/ph in one second !!! • Because this type of acceleration requires huge amounts of force, sprint/ power athletes have a lot more muscle than long- distance/ endurance athletes

  22. ACCELERATION Acceleration can’t last for the duration of an event…..even a sprint !!! In a 100m sprint the runners accelerate out of the blocks (positive acceleration) until they reach max speed. At this speed there is no change in the rate of velocity(zero acceleration) until they begin to slow down at the end of the sprint (negative acceleration)

  23. CONSERVATION OF MOMENTUM • This principle applies to any collision between two objects. • Eg: A foot contacting the ground in running, a bat hitting a ball or two balls colliding (pool / billiards). ** When a collision occurs: the total momentum of two bodies before impact is equal to the total momentum after impact

  24. CONSERVATION OF MOMENTUM This is best explained by Newton’s 3rd Law: “For every action, there is an equal and oppositereaction” For example, when playing pool the white ball hits a coloured ball and stops on impact. The momentumpasses onto the coloured ball which then moves.

  25. CONSERVATION OF MOMENTUM Basically explained: when the white ball applies a force to the next ball, that other ball will react with the same forceinanother direction. Another Example = 10 Pin Bowling Ball hits the pins….pins go flying…!

  26. ELASTICITY Elasticity = the ability of surfaces to “give”then return to their original shape Surfaces with more elasticity result in less energy being lost on impact because they rebound to their original position quicker. Eg: A tennis ball will bounce higher from a surface such as ‘rebound ace’ than a grass tennis court

  27. ELASTICITY Rebound Ace (Australian Tennis Open) is more elastic than a Grass Court (Wimbledon). A new tennis ball has greater elasticity than a soft, flat one and therefore it will bounce higher and return to shape quicker. This is advantageous to a tennis player because they can generate more velocity when the racquet and ball collide.

  28. ELASTICITY The temperature of the ball can also affect it’s elasticity. The hotter a ball is, the more elasticity it will have. Eg: Squash players rub the ball between their foot and the court before they serve to heat up the ball. It can then be hit harder.

  29. DRAG Drag = Disturbed air that creates a resistance force opposing the movement of a projectile through the air Eg: How a tennis ball has more drag than a cricket ball due to the fur on it’s surface

  30. NEWTON’S LAWS Newton has 3 laws of motion: • Law of Inertia • Law of Acceleration • Law of Action / Reaction

  31. “An object will remain in its current state of motion (stationary or moving) unlessacted upon by a force.” 1st LAW

  32. Force = Mass x Acceleration “The greater the mass of an object, then thegreater force required to change its state of motion (stationary or moving)” OR “The acceleration of a body is directly proportional to the size of the force applied and in the direction of the force applied.” 2nd LAW

  33. 3rd LAW “For every action there is an equal and oppositereaction”

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