3.1b Levers, Stability, and Technology

Centre of Mass

• the point at which a body is balanced in all directions

• the point where the weight of the body is usually concentrated

• often in the middle, especially in round objects

• if an athlete raises their arms, the CoM will also be raised

• can be outside the body and act as a point of rotation

Stability

• ability of the body to resist motion and remain at rest

• ability to withstand a force applied and return to the original position

Factors affecting stability

Maximising and Minimising Stability

• in a sprint start, the sprinter preparing in the blocks has maximal stability

• when ‘set’ is called, the sprinter lifts their hips, raising their CoM, lifts one knee, reducing points of contact, and leans forward, minimising stability ready for movement to occur

• when the starting gun is fired, instability is maximised to aid performance - the chest lifts, raising the centre of mass, the athletes hand come off the track, and their line of gravity falls inside their base of support, causing the body to fall forwards

• this is prevented by driving one leg forwards with great speed, which minimises movement time

Levers

• generate muscular effort to overcome a given load

• increase the speed of a given movement

Components

Class

First Class

• fulcrum is in the middle - EFL or LFE

• extension of the neck when preparing to head a football

Second Class

• load is in the middle - ELF or FLE

• ball of the foot when rising on to tiptoes in diving

Third Class

• effort is in the middle - FEL or LFE

• flexion of the elbow during a biceps curl

Efficiency of the lever system

• effort arm - distance from the fulcrum to the effort

• load arm - distance from the fulcrum to the load

• longer levers generate greater forces as the load arm become longer and so can give greater acceleration to projectiles

• the length of the effort and load arms will give a mechanical advantage or disadvantage

  • second class levers always have mechanical advantage - effort arm is longer than the load arm

    • move a large load with little effort

  • third class levers will always have mechanical disadvantage - load arm is longer than the effort arm

    • large effort is required to move a small load

  • first class levers can have either - depends which arm the fulcrum is closer to

Technology