Chapter Five : Biomechanical Principles of Equilibrium

Question 1

Equilibrium definition

Answer 1

When an object has no unbalanced forces or torques acting on it
Either motionless or moving at a constant velocity

Question 2

Static equilibrium definition

Answer 2

When an object is motionless. All the forces and torques acting on the body add up to zero

Question 3

Three conditions for static equilibrium

Answer 3

1. The sum of all the vertical forces acting on the body must be zero
2. The sum of all the horizontal forces acting on the body must be zero
3. The sum of all the torques must be zero

Question 4

Dynamic equilibrium definition

Answer 4

When the body or an object is moving with a constant velocity

Question 5

Stability definition

Answer 5

Is the resistance to the disruption of the equilibrium

Question 6

Balance definition

Answer 6

Is the ability to control equilibrium while stationary or moving

Question 7

Correlation between balance and stability

Answer 7

Higher stability objects have more balance, lower stability objects have less balance

Question 8

Factors affecting stability

Answer 8

Base of support
Centre of gravity
Line of gravity
Body mass
Friction between the body and the surface

Question 9

Base of support definition

Answer 9

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

Question 10

Relationship between base of support and stability

Answer 10

The larger the base of support the greater the stability

The smaller the base of support the lesser the stability

Question 11

Increasing base of support examples

Answer 11

Boxer widening his stance
Baseball player spreading his legs
Cricketer moving one leg forward

Question 12

Decreasing base of support examples

Answer 12

Swimmers lean on tiptoes to allow an easier takeoff in diving
A dancer on one foot has less stability to allow them to complete turns easier
Sprinter leaning on tiptoes to allow them to takeoff quickly

Question 13

Centre of gravity definition

Answer 13

The point at which the whole weight of an object can be considered to act

Question 14

How does the centre of gravity change?

Answer 14

When moving upwards (tiptoes) the centre of gravity moves upwards
When crouching down the centre of gravity is lowered

Question 15

Relationship between the centre of gravity and stability

Answer 15

When the centre of gravity is raised the stability is decreased
When the centre of gravity is lowered the stability increases

Question 16

Raising centre of gravity to decrease stability examples

Answer 16

Divers on their tiptoes to initiate diving quicker
Runners begin on their toes to initiate a quicker takeoff
Dancers perform on their toes to allow easier turns

Question 17

Lowering centre of gravity to increase stability examples

Answer 17

Wrestler crouching down when against opponent
Surfer crouching down on the board to maintain stability
Boxer crouching down to brace himself

Question 18

Locating the centre of gravity

Answer 18

Usually sits near he navel
When the mass has uniformly distributed the centre of gravity will be in the exact centre
When the mass inst uniformly distributed the centre of gravity will shift towards the direction of greatest mass

Question 19

Line of gravity definition

Answer 19

A theoretical line that passes through the centre of gravity in the direction that gravity acts

Question 20

The relationship between the line of gravity and stability

Answer 20

When the line of gravity acts through the centre of the base of support the stability is increased
Moving the line of gravity to the edge or the outside of the base of support decreases stability

Question 21

Examples of moving the line of gravity outside the base of support

Answer 21

Swimmers leaning over on their blocks to initiate dives easier
Sprinters leaning over blocks to initiate run easier
Rugby players leaning forward to create more resistance against their opposition

Question 22

The relationship between body mass and stability

Answer 22

The greater the mass of the body the higher the stability as it requires more force to move them
The lighter the mass of the body the lower the stability as it takes less force to disrupt equilibrium

Question 23

Increasing mass for stability examples

Answer 23

A wrestler has an advantage of being heavier as it will be harder to move them
A rugby player having a greater mass will allow them to have more stability against opponents

Question 24

Decreasing mass for stability examples

Answer 24

A dancer having a lighter mass so they can perform movements easier
A gymnast having a lighter mass so they can perform movements easier

Question 25

The relationship between friction and stability

Answer 25

Increasing the friction between a body and a surface will increase stability

Question 26

Examples of increasing friction for stability

Answer 26

Surfer using wax on their board A golfer using gloves A footy player wearing studs on their boots

Question 27

Lever definition

Answer 27

Is a simple machine consisting of a rigid bar that can be made to rotate around an axis in order to exert a force on another object

Question 28

What does the mechanical advantage of a lever do?

Answer 28

Allow us to apply a small force to mover a much greater resistance To move one point of an object a small distance, causing another point of the same object to move a relatively larger distance

Question 29

3 parts of a lever

Answer 29

``` An axis (fulcrum or pivot point) A resistance (weight or load to be moved)\ A force ```

Question 30

First class lever definition

Answer 30

When the resistance and the force are on either side of the axis FAR

Question 31

Second class levers definition

Answer 31

The resistance is between the force and the axis | ARF

Question 32

Third class lever definition

Answer 32

The force is between the resistance and the axis | AFR

Question 33

Mechanical advantage definition

Answer 33

The ratio of the force arm to the resistance arm

Question 34

Mechanical advantage equation

Answer 34

Mechanical advantage = Force arm / Resistance arm

Question 35

Force arm definition

Answer 35

Is the distance from the axis to the force

Question 36

Resistance arm definition

Answer 36

Is the distance from the axis to the resistance

Question 37

Mechanical advantage values

Answer 37

> 1 - Requires less effort to move a resistance | < 1 - Increased range of motion and increases angular speed

Question 38

Lever length in sport

Answer 38

Anatomical levers are often extended through a racquet or club. This creates a longer resistance arm A greater force is required to move it but it increases the range of motion and therefore angular velocity allowing the ball to be hit further.

Question 39

First class lever summary

Answer 39

``` FAR force and resistance applied in same direction MA- centre =1, resistance >1, force<1 Centre head extension Scissors ```

Question 40

Second class lever summary

Answer 40

``` ARF small force needed to overcome large resistance MA >1 resistance arm < force arm Heel raise (axis is toe) ```

Question 41

Third class lever summary

Answer 41

``` AFR large forces needed to overcome small resistance <1 force arm < resistance arm bicep curl ```