AS A Level Sport and Physical Education

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• AS / A Level Sport and Physical Education
• Force

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FORCE

• FORCE
• FORCE is push or pull
• the unit is the NEWTON (10 N is approx the weight
  of 1 kg)
• force changes the state of motion of an object
• force causes acceleration or deceleration or
  change of direction
• the more force the bigger the acceleration
• force changes the shape of an object

• DEFINITION OF THE NEWTON
• one newton of force is the force required
• to produce an acceleration of 1 ms-2
• in a mass of 1 kg
• this is related to the inertial property of mass
• the more force applied, the more acceleration
  produced
• see Newtons second law, F m x a

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FORCE

• PROPERTIES OF FORCE
• force has direction and size (value)
• and is therefore a VECTOR
• when describing a force it is important to
  explain where the force acts (the point of
  action)
• as well as the direction

• NET FORCE
• net force is the result of all forces added
  together taking the direction into account (see
  VECTORS)
• net force forwards produces acceleration -
  positive
• net force backwards produces deceleration -
  negative
• net force sideways produces change of direction

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FORCE

• EXAMPLES - NET FORCES
• sprinter accelerating
• jumper taking off
• projectile in flight
• jumper landing
• as feet make contact with ground
• net force backwards causes deceleration

• EXAMPLES - ZERO NET FORCE
• sprinter at full speed
• swimmer at full speed

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PIN MEN - FREE BODY DIAGRAMS

• SHAPE OF BODY
• should be represented approximately
• FORCES ACTING
• forces are represented by arrows
• in the direction of the force
• the point of action of the force should be shown
  where the force acts
• at the foot
• on the body
• on the hand
• the length of the arrow represents the size of
  the force

• DIAGRAM
• shows force in black acting downwards on the
  ground

• force in red acting upwards on the jumpers foot

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TYPES OF FORCE ACTING ON A SPORT PERFORMER
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FORCE

• EXAMPLE - NET FORCES - THE HIGH JUMPER AT TAKE
  OFF
• the net force is made up from a number of forces
  which add together
• in the case of the high jumper taking off the
  following forces act

• his weight (acting downwards)

• the reaction force acting upwards

• and a friction force acting backwards

• these forces add up to a net force as shown

• which will cause upward acceleration - for
  take-off
• and forward rotation (over the bar)

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PIN MEN - FREE BODY DIAGRAMS

• DIAGRAM
• shows four forces acting
• 2 forces acting up on the foot and down on the
  body

• FORCES ACTING
• forces are represented by arrows
• in the direction of the force
• the point of action of the force should be shown
  where the force acts
• at the foot
• on the body
• on the hand
• the length of the arrow represents the size of
  the force

• 2 forces acting backwards on the body and
  forwards on the foot
• longer arrows mean greater force

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MOMENTUM

• MOMENTUM
• a concept derived from Newton's second law which
  says
• force rate of change of momentum
• (Linear) momentum mass x velocity
• linear means in a straight line
• momentum includes both mass and velocity
• so an object which has a lot of momentum requires
  a lot of force to stop it
• which is a good argument for fast heavy rugby
  players or American footballers
• momentum is a vector (and therefore has direction)