Chapter 5: Biomechanic Principles of Equilibrium

Question 1

Equilibrium

Answer 1

an object that has no unbalanced forces or torques acting upon it

Question 2

Dynamic Equilibrium

Answer 2

when an object or body is moving with a constant velocity and has no change in speed or direction

Question 3

Static Equilibrium

Answer 3

when an object has no movement or rotation

Question 4

Balance

Answer 4

the ability to control equilibrium

Question 5

Stability

Answer 5

the resistance to the disruption of equilibrium

- Sports we want to increase stability E.g. Wresting
- Sports we want to decrease stability E.g. Starting blocks in swimming

Question 6

Factors that affect Stability

Answer 6

• Base of support
  
  • Centre of gravity
  • Line of gravity
  • Body mass
    
    • Friction between the body and the contacting surfaces

Question 7

Base of Support

Answer 7

the area bound by the outside edges of the body parts in contact with the supporting surface

- The greater the BOS = the greater the stability

Ways to increase BOS:

- Spread feet wider
- Crouching over
- Placing hands on the floor
    - Leaning against an object

Question 8

Center of Gravity

Answer 8

the point around which the weight is balanced

- Can be manipulated by moving your body into different positions
- The lower your COG, the more stable you are
- COG can fall outside a persons body e.g. When you lean forward

Question 9

Line of Gravity

Answer 9

the direction in which the gravity acts

• When the line of gravity is in the centre of the BOS, stability is the greatest

Question 10

Body Mass

Answer 10

• The greater the mass of body, the greater the stability

- Beneficial in sports such as wrestling

Question 11

Friction

Answer 11

• Increased Friction can increase stability

E.g. Surfboard wax increases friction between surfers feet and board

Question 12

Levers

Answer 12

a simple machine consisting of a rigid bar, an axis to rotate around, a force and a resistance.

- A lever rotates around an axis when force is applied causing the lever to move against a resistance 
    - A lever system can be used to either multiply force or produce range of motion and multiply speed

Question 13

Levers are made up of(in the body)

Answer 13

• The axis: a fixed joint in the body
  
  • The force(effort): muscles that contract to generate force to move a lever
    
    • The resistance: the bone of the body and whatever is being held or moved by the bone

Question 14

Mechanical Advantage

Answer 14

the measurement of whether a lever is designed to multiply force or multiply speed

- Calculated by force arm(distance from axis to force) / resistance arm(distance from axis to resistance)
- Increased mechanical advantage(>1) will improve the ability to move a heavy resistance (multiply force)
    - Decreased Mechanical advantage(<1) will improve the ability to move it in a full range of motion and multiply the speed

Question 15

Force Arm(FA)

Answer 15

distance between force and axis

Increased FA = increased force

Question 16

Resistance Arm(RA)

Answer 16

Distance between resistance and axis

Increased RA = increased range of motion and speed

Question 17

First Class Lever

Answer 17

R.A.F

• If axis in the middle = MA of = 1
• If axis near force - for speed and ROM = MA of <1
• If Axis near resistance - for force motion = MA of >1
• E.g. Neck

Question 18

Second Class lever

Answer 18

A.R.F

• for force motion(large resistance can be moved easily) = MA >1
• E.g. Calf Raise

Question 19

Third Class Lever

Answer 19

A.F.R

• For speed and ROM(requires large force to move relatively small resistance) = MA <1
• E.g. Bicep Curl