centre of mass Flashcards
centre of mass
point at which a body is balanced in all directions and from which weight/ gravity appears to act
where is the centre of mass in the human body
about the belly button
is the centre of mass always in the same position
- it isn’t a fixed point
- it alters as a person changed their body position
what happens when both arms are raised up to COM
it is raised
what happens to COM when someone bends forwards
it moves forwards and down
what is the location of the centre of mass dependent on
the distribution of body mass
why is centre of mass manipulated
to improve technique by altering body position
what is the COM of a symmetrical object e.g football
it’s actual centre
where can the centre of mass move to
the outside of a body
where is the centre of mass of any object
where the mass of the object is concentrated
is the centre of mass a fixed point
- no, it is moveable
as the body moves what happens to COM
it moves
stability
- the ability to resist motion and remain at rest
- to withstand force and return to its original position
which 2 ways is centre of mass position important
- balance
- rotation
what is COM dependent on
- COM: height of the centre of mass
- Base of support: number of bases of support
- Line of gravity: position of the line of gravity
- Mass : mass of the body
how stable is a sumo squat wrestler ?
- COM: height has decreased, increasing stability
- BOS: 2 bases, increasing stability and a wider stance
- LOG: is further within the BOS increasing stability and shorter to ground
- Mass: increased stability as sumo wrestler has greater body mass
the lower the centre of mass the what
more stable the performer
why does a gymnast flex the hip and knee after a vault landing
- COM: lower
- LOG: shorter - widening base of support
- LOG further within BOS
- providing a more stable landing
why do judo performers have a wide stance
- COM: lower / shortened LOG
- BOS wider so LOG further within BOS so position is more stable
- increasing the difficulty to be thrown
the greater the size of base of support the greater the what
stability
why is the bridge a stable balance
- BOS is increased in size by having 4 contact points
- COM is lower to the ground and BOS is further within BOS / LOG is shorter
- increasing stability of the balance
line of gravity
an imaginary line extending from the COM to the ground
an object will stay stable as long as the line of gravity from the COM stays within what
base of support
the more central the line of gravity is to the base of support the what
greater the stability
mass of the body
greater the mass of a body the greater it’s inertia and greater it’s stability
why does the rugby prop have good stability
- increased body mass increased stability due to an increased equal and opposite reaction force
- enables them to withstand a force
- decreased height: lower COM and shorter LOG
if the Log is outside the BOS the body will be what
unstable
eccentric force
- the line of gravity moves outside of the base of support
- the force of gravity and mass of the body act upon the COM
- causing the body to become unstable and topple over
how do we make COM more stable
- make it low / short log
how can we make BOS more stable
increase contact points of bases of support
how can we make line of gravity more stable
- is further within the base of support = more stable
how does mass increase stability
bigger mass = more stable
how is a sprinter stable in the crouched position in the blocks
- low COM as she’s in a crouch
- more points of base of support x5 = more stable
- line of gravity is further within base of support
- sprinter has a higher muscle mass = greater reaction force
how does the sprinter minimize stability when the gun is fired
- chest is lifted raising COM
- hands leave the track reducing the points of contact and bases of support
- line of gravity moves forwards outside the base of support resulting in body falling forwards
as the LOG has moved outside the base of support what does the sprinter need to do
- drive one leg forward with great speed
- movement time is minimized giving a perfect start to the race
how can a high jumper manipulate the body shape and location of COM to maximize performance
- uses ‘J curve’ to allow a greater velocity in this approach
- plants the outside foot allowing the inside leg to lift with the arms at take off raising the COM as high as possible
- back is in hyper extension
- weight of legs and head are below the hips
- this makes the COM move below the body
- Fosbury flop is in a more efficient position as COM travels under the bar while the jumper clears the bar
- only 1 part of the body has to be above the bar at any one time
