balance/stability

• what is equilibrium?

  when all forces are balanced (all forces acting upon the body/object add up to zero)

  • either: motionless (static) or moving with a constant velocity (dymanic)
  • static equilibrium - completely motionless (no moving or rotation)
  • dynamic equilibrium - constant velocity (no acceleration)
• what is stability?

  the degree to which a body resists changing it equilibrium

  • greater stability -> harder to unbalance object
  • less stability -> easier to unbalance object
  • can increase or decrease stability to improve performance
• what is balance?


  the ability to control the state of equilibrium

  • require a good level of balance to control equilibrium
• what factors can be manipulated to influence stability?

  • base of support
  • centre of gravity
  • line of gravity
  • friction
  • mass
• what is base of support?

  define: area bound by the outside edges of the body parts in contact with the supporting surface

  • bigger base of support -> greater stability
• whawt is centre of gravity?

  define: central point of an object/body where all of its weight is evenly distributed and balanced (point shifts with every movement of body)

  • lower centre of gravity -> greater stability
• what is line of gravity?

  • gravity acts on body through centre of gravity - direction of this is referred to as the line of gravity
  • when line of gravity acts through base of support -> greater stability
  • when line of gravity acts outside of the base of support -> less stability
• what is friction?

  define: force between two surfaces and opposes the direction of motion

  • greater friction between body and surace it is in contact with (base of support) -> greater stability
• how does mass impact stability?

  • greater mass -> greater force required to move it (disrupt equilibrium)
  • greater mass -> greater stability
• what is a lever?

  define: rigid structure that rotates around an axis

  • has three parts: axis + resistance + force
  • class of lever is determined by position of three components (different levers do different things)
  • levers are used to increase performance in sport (most of the time use third class levers)
  • anatomical levers can provide a mechanical advantage

  *axis = pivot point/ rotation in the lever

  *force = point in the lever where a force is applied

  *reistance = point in the lever where there is resistance
• what is a first class lever?

  the force and the resistance are on either side of the axis (think: seesaw)

  *note arrow direction

  
• what is a second class lever?

  when the resistance is between the force and the axis

  
• what is a third class lever?

  when the force is located between the resistance and the axis

  
• how can we increase stability?

  • lower an object's centre of gravity
  • ensure the line of gravity is over the base of support
  • increase the size of the base of support
  • increase the friction between the surfaces
  • increase the mass of an object
• how can we decrease stability?

  • raise an object's centre of gravity
  • shifting the line of gravity outside the base of support
  • narrowing the base of support
  • decreasing the friction between surfaces
  • decreasing the mass of an object
• what is mechanical advantage?

  define: the degree to which a lever amplifies force production

  equation: mechanical advantage = force arm / resistance arm
• what is the force arm?

  the distance between the axis and the force
• what is the resistance arm?

  the distance between the axis and the resistance
• for second class levers:

  if the force arm > resistance arm -> mechanical advantage > 1

  • allows you to move large mass with a small force (amplifies force)
• for third class levers:

  if resistance arm > force arm -> mechanical advantage < 1

  • allows you to move the lever with a greater range of motion (amplifies velocity/speed)