equilibrium

• static equilibrium

  when an object is stationary and all the forces or torques acting on it total to zero.​

  3 key conditions:​

  • sum of all vertical forces acting on the body must be zero​
  • sum of all horizontal forces acting on the body must be zero​
  • sum of all torques must be zero​
• dynamic equilibrium 


  when an object is moving with constant velocity and is ​not changing its state of motion (speed nor direction)
• stability

  the resistance to the disruption of the equilibrium (ability to deal with a disturbance)

  increase stability to improve performance :                           ​

  wrestling, gymnastics, ice skating

  decrease stability to improve performance :                    ​

  sprint start, diving
• balance 


  the ability to control equilibrium (ability to maintain the COG over BOS)
• factors affecting stability - COG

  centre of gravity-

  the point around which its weight is balanced

  -lowering the COG improves stability
• factors affecting stability - LOG

  line of gravity-

  imaginary line between the COG in the path of gravity (to the ground)
• factors affecting stability - BOS


  the area of an object that is in contact with the surface supporting it

  -larger, widen stance to improve stability
• factors affecting stability - mass

  a body with a larger mass will be more stable as it has greater inertia, and will require a greater force to move it.​

  eg. a sumo wrestler is hard to push out of the ring
• increasing stability

  tips-

  • increase the size of BOS (widen stance)​
  • ​extend BOS in the direction of the oncoming force
  • ​crouch down to lower your COG
  • ​ensure COG falls within BOS
  • shift your LOG towards the oncoming force
  • ​increase friction between body and the surface or surfaces contacted
  • increase mass
• factors affecting stability - friction


  stability will be increased when the friction between the athlete and the contact surface is increased. 

  eg. stops on a football boot, wax on a surfboard​