Centre of Mass and Stability Flashcards
Definition of centre of mass
The point at which a body is balanced in all directions, the point from which weight appears to act
Where is an athletes COM is they stand in an anatomical position?
around their naval (bellybutton)
What happens to the cOM is athlete raises their arms?
cOM is raised
Where is the centre of mass for a gymnast performing a front tucked somersault?
In front of their body, they rotate around it
How is the Fosbury Flop technique used to manipulate cOM?
-Uses a J-curve to allow greater velocity in the approach
-Plants outside foot to allow the inside leg to lift, along with the arms, at take off to raise the centre of mass as high as possible
-Full extends spine to rotate around the bar moving the cOM outside the body and below the bar
-Because the cOM is beneath this technique requires less force at take-off to clear the same heights as earlier techniques
Definition of stability
The ability of a body to resist motion and remain at rest
AND
Ability of body to withstand a force applied and return to its original position without damage
State the factors affecting stability
- Mass of body
- Height of centre of mass
- Base of support
- Line of gravity
Explain the factors affecting stability with examples
- Mass of body - the greater the mass of a body, the greater its inertia and therefore the greater its stability
eg. sumo wrestlers have a high mass - Height of cOM - the lower the centre of mass, the greater the stability
eg. when a gymnast lands, they flex at the hip and knee to low their cOM and have stable landing, martial arts performers sit with a low wide stance in defensive situations - Base of support - the greater the base of support, the greater the stability
eg. two feet and two hands in a gymnasts bridge position, table tennis player stands with feet wider than shoulder width - Line of gravity - the more central the line of gravity to the base of support the greater the stability
eg. a netball goal shooters line of gravity falls within her base of support whereas a goalkeeper who is marking the shots centre of mass falls outside and in front of her base of support, leading to over-rotation
In what ways can base of support be widened?
Moving two points of contact (feet) wider apart, creating a large surface ares by increasing the number of contact points
What is the line of gravity?
An imaginary line which extends from the centre of mass downwards to the floor
How does a sprinter maximise stability?
Preparing in the blocks, they have maximum stability. The crouched position gives a low centre of mass, the base of support is large with 5 points of contact (2 hands, 2 feet, 1 knee), the line of gravity falls within the base of support and sprinters typically have a high mass due to their proportion of muscle mass
How does a sprinter minimise stability?
-When set is called, they lift their hips, raising their centre of mass, lifts one knee reducing points of contact, and leans forward shifting line of gravity to edge of base of support. This reduces stability ready for movement
-When gun is fired, instability maximised, the chest lifts raising the centre of mass, hands come off the track minimising the base of support and the points of contact, the line of gravity falls in front of base of support causing body to fall forwards =
When can having instability be beneficial in sport?
-When changing direction
eg. moving line of gravity outside of base of support to dodge in netball, swerve in rugby
-Rotating
eg. gymnast leans forward and raises arms in take-off for front somersault to raise cOM and move line of gravity in front of base of support
-Increasing range of motion of stretch
eg. goalkeeper in netball outstretched to defend a shot has a high cOM, reduced points of contact, line of gravity falls in front of base of support
