4. Centre of Mass

Question 1

What is centre of mass?

Answer 1

The point at which a body is balanced in all directions.
The point from which weight appears to act.

Question 2

Which sporting example can centre of mass be applied to?

Answer 2

High jump

Question 3

What is the fosbury flop technique?

Answer 3

• uses a j-curve approach
• plants the outside foot
• drives arm up, lifting the centre of mass
• fully extends the spine to rotate around the bar
• centre of mass passes under the bar

Question 4

What is stability?

Answer 4

The ability of a body to resist motion and remain at rest.

Question 5

What are the factors affecting stability?

Answer 5

• mass of the body
• height of the centre of mass
• base of support
• line of gravity

Question 6

How do you maximise stability? (sprint start on your marks)

Answer 6

• a sprinter preparing in the blocks has maximum stability
• crouched position gives low centre of mass
• the base of support is large, with 5 points of contact
• the line of gravity falls within the middle of the base of support and sprinters typically have a high centre of mass due to their high proportion of muscle mass

Question 7

How do you minimise stability (sprint start set)?

Answer 7

• when set is called, sprinter lifts hips, raising centre of mass
• lifts one knee, reducing points of contact and leans forward, shifting line of gravity to edge of base of support
• COM moves forward to front of base of support
• reduces stability ready for movement
• when gun is fired, instability is maximised to aid performance as the centre of mass falls out of the base of support
• performers own weight supports the movement forward