Balance

• Static (not moving)
• Dynamic (moving)

• Stability is the degree to which a person can resist loss of balance
• Stability depends on 3 factors:
• area of supporting base
• height of center of mass or (COM) center of gravity (COG) above base
• vertical position of the COM within/outside the base of support
• Stability is increased by:
• widening base of support
• lowering COM
• having vertical line from COM fall closer to the center of the support base
Movement is enhanced by moving the COM above and/or away from the support base
• "Free" limbs aid stability by acting as counterbalances

Force

• A force is a PUSH or a PULL
• It is a scalar quantity - (scalar = amount)
• Quantities such as force may be scalar or vector quantities
• vector quantities include magnitude and distance
• it is helpful for physical educators to understand forces
• application of force
• direction of force
• line of force relative to the COM of the object acted upon

 

• An object at rest or in motion will remain so unless acted upon by a force
• a soccer ball at rest will not move unless kicked
• a soccer ball in motion in the air will fall to the ground
• Resistance to force is proportional to the mass (amount of matter in) an object
• Inertia
• F=ma
• a beach ball needs less force to move it than a soccer ball
• Every action has an equal and opposite reaction
• ground reaction forces result in movement in running, etc.
• more force applied to the ground = more ground reaction forces
• stronger/more powerful muscles increase speed
• arm swing increases leg forces

Application of Force (throwing and striking)

• The resultant movement of an object depends on:
• point of application of force
• direction of force
• line of force relative to center of mass
• line of force through the COM
• mass of the objects
• Momentum
• momentum is the mass of an object multiplied by it's velocity
• momentum = mv
• momentum of one object can be transferred to another object
• throwing
• striking
• to maximize amount of momentum transferred:
• maximize velocity of throwing or striking arm
• minimize the reduction in velocity/momentum around the point of contact/release
• optimize the mass of the striking implement
• transfer momentum from lever to lever
• step in, rotate, throw
• step out

Absorption of force (catching and landing)

• F=ma
• Force is absorbed proportionally to:
• distance or "give"
• move in direction of object to be caught
• reach for object to be caught
• allow object to move towards body after catching
• area
• land on both feet, toes then heels
• bend knees after contact with ground

• The body is a system of levers, mostly 3rd class:
• class 1 = FORCE - FULCRUM - RESISTANCE
• teeter totter
• head
• class 3 = FULCRUM - FORCE - RESISTANCE
• catapault
• limbs (compound)
• class 2 = FULCRUM - RESISTANCE - FORCE
• wheelbarrow
• foot

Locomotor patterns

• walk
• one foot in contact with ground
  
• run
• period of flight between steps -  no feet in contact with ground
  
• hop
• take off from one foot, land on same foot
  
• jump
• take off from one foot or both feet, land on both feet
  
• leap
• take off from one foot, land on opposite foot
• gallop
• rear foot does not cross lead foot - "heel -toe"
  
• slide
• side step, trail leg does not cross lead leg
  
• skip
• step-hop combination