Centre of mass and stability

Centre of mass, base of support and balance, from judo to the Fosbury flop.

The outline, topic by topic

Each topic is weighted the way the exam weighs it.

Centre of mass: what is it?
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The point where the whole body's mass can be considered concentrated.
Standing, it lies just in front of the second sacral vertebra, at about 55% of height from the ground.
A judoka wants to be harder to unbalance. What does he do?
- He bends his legs and widens his stance
- He goes onto his toes
- He brings his feet together
- He leans back
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He bends his legs and widens his stance
A low centre of mass and wide base raise stability.
Base of support: what is it?
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The area enclosed by the points of contact with the ground.
Spreading the feet enlarges it.
Why does a sprinter deliberately go off balance at the start?
- To be more stable in the blocks
- To reduce air resistance at the start
- Projecting the centre of mass ahead of the feet helps acceleration
- To push less on the blocks
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Projecting the centre of mass ahead of the feet helps acceleration
Stability is not always wanted: movement needs imbalance.
Static balance: what is it?
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Balance holds as long as the centre of mass projects inside the base of support.
Otherwise one falls or steps.