Biomechanical principles: stability and lever systems

Question 1

Centre of mass definition:

Answer 1

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

Question 2

Factors that affect stability:

Answer 2

• Mass of the body
• Height of the centre of mass
• Base of support
• Line of gravity

Question 3

When can being unstable in sport be an advantage?

Answer 3

• When changing direction e.g. rugby
• Rotating e.g. A somersault in gymnastics
• Increasing range of motion or stretch e.g. a goalkeeper in netball.

Question 4

What is the definition of stability?

Answer 4

The ability of a body to resist motion and remain at rest, or for a body to withstand a force applied and return to its original position without damage.

Question 5

How does mass of the body affect stability?

Answer 5

The greater the mass of a body the greater its inertia, and therefore the greater its stability.
E.g. Sumo wrestler + Props

Question 6

How does the height of centre of mass affect stability?

Answer 6

The lower the centre of mass the greater the stability.

Question 7

How does the base of support affect stability?

Answer 7

The greater the size of the base of support the greater the stability. This can be done by moving 2 points of contact further apart or by adding more points of contact.

Question 8

How does the line of gravity affect stability?

Answer 8

The line of gravity is an imaginary line which extends from the centre of mass down to the floor.
The more central the line of gravity to the base of support the greater the stability.

Question 9

What are the components of a lever system?

Answer 9

Lever - Bone
Fulcrum - Joint
Effort - Muscular force
Load - Weight or resistance

Question 10

What is a 1st class lever?

Answer 10

The fulcrum is in the middle
E-F-L
L-F-E

Question 11

What is a second class lever?

Answer 11

The load is in the middle
E-L-F
F-L-E

Question 12

What is a third class lever?

Answer 12

The Effort is in the middle
L-E-F
F-E-L

Question 13

What is an example of a first class lever in the body?

Answer 13

Extension of the neck when preparing to head a football.

Question 14

What is an example of a second class lever in the body?

Answer 14

Ball of foot in the take off phase of a high-jump.

Question 15

What is an example of a third class lever in the body?

Answer 15

Flexion of the elbow during a bicep curl.

Question 16

What is the effort arm?

Answer 16

The distance from the fulcrum to the effort.

Question 17

What is the load arm?

Answer 17

The distance from the load to the fulcrum.

Question 18

What is a mechanical advantage?

Answer 18

Second class lever systems where the effort arm is greater than the load arm.

A large load can be moved with relatively small effort.

Question 19

What is a mechanical disadvantage?

Answer 19

Third class lever systems where the load arm is greater than the effort arm.

A large effort is required to move a relatively small load.