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 - mass of body

the greater the mass, the greater the inertia

Factors affecting stability - height of centre of mass

the lower the centre of mass, the greater the stability

Factors affecting stability - base of support

the greater the size of the base of support, the greater the stability - can also be increased by adding more points of contact

Factors affecting stability - line of gravity

the more central the line of gravity to the base of support, the greater the stability

Using stability

	the greater the mass, the greater the inertia
Height of centre of mass	the lower the centre of mass, the greater the stability
Base of support	the greater the size of the base of support, the greater the stability - can also be increased by adding more points of contact
Line of gravity	the more central the line of gravity to the base of support, the greater the 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

First class lever

• fulcrum is in the middle - EFL or LFE

• extension of the neck when preparing to head a football

Second class lever

• load is in the middle - ELF or FLE

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

Third class lever

• effort is in the middle - FEL or LFE

• flexion of the elbow during a biceps curl

Efficiency of a 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

Mechanical advantage and 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

Limb kinematics

• Study of movement in relation to time and space

• 3D or optical movement analysis records an athlete performing a sporting action, allowing the efficiency of the movement to be evaluated

• Data produced can be used by coaches to improve performance/ specific techniques of athletes

Force plates

• Ground reaction forces are measured in laboratory conditions using force plates

• Athletes balance, run, and jump on a force plate which assesses the size and direction of forces acting on the athlete, acceleration rates, and work and power outputs

• Used for sports biomechanics assessment, gait analysis, balance rehabilitation, and physical therapy

Wind tunnels

• Steel frame buildings containing wide fand, where artificial wind is produced

• Technology is used to develop the drag reduction system. Objects such as F1 cars and cycling helmets can be tested for aerodynamic efficiency

• Engineers study the flow of air around the object. The aim is to improve the flow of air around an object, streamlining its path through the oncoming air, and potentially increasing lift or decreasing drag