Chapter 5

Question 1

Equilibrium

Answer 1

Where an object has no unbalanced forces or torques acting upon it
Objects in equilibrium are either motionless or moving at a constant velocity
Controlling equilibrium is crucial in some sports

Question 2

Static Equilibrium

Answer 2

an object is not moving or rotating

all forces add to 0

Question 3

For Static Equilibrium to be achieved, these conditions must be met:

Answer 3

1. Vertical force sum must equal 0
2. Horizontal force sum must be equal 0
3. Torque force sum must equal 0

Question 4

Dynamic Equilibrium

Answer 4

an object is moving at a constant velocity

there must be no change in speed or direction

Question 5

Stability

Answer 5

the resistance to disrupt equilibrium

Question 6

Balance

Answer 6

the ability to control equilibrium

Question 7

A body’s ability to maintain equilibrium is affected by:

Answer 7

Base of support
Centre of gravity
Body Mass
Friction between the body and the surface or surfaces contacted

Question 8

Base of Support…

Answer 8

• BOS is bound by the area around the outside edges of the body parts
• generally a larger base of support leads to a great stability

Question 9

Increasing Base of Support…

Answer 9

• as BOS increases, the degree of muscular effort decreases

- increasing BOS can be as simple as moving feet further apart

Question 10

How can Base of Support be increased?

Answer 10

• Having one foot in front of the other increases backwards and forwards stability
• Having one foot away from the midline increases side to side stability

Question 11

Give an example of how Base of Support can be increased?

Answer 11

Baseball players will hit with one foot in front of the other so they can maintain balance whilst hitting hard

Question 12

Explain and give an example of Base of Support being very small

Answer 12

Sometimes the BOS is very small, thus a movement of the line of gravity outside the body’s line of support will lead to a loss of balance
eg balance beam in gymnastics or tightrope walking

Question 13

Centre of Gravity

Answer 13

Refers to the point in which weight is balanced, disregarding the position of the body. Generally found near the navel

Question 14

How do you increase centre of gravity?

Answer 14

-Lowering COG eg bending knees, flexing hips and ankles

Question 15

How do you decrease centre of gravity?

Answer 15

raising the COG eg lifting arms up

Question 16

In a symmetrical object, where is the centre of gravity located?

Answer 16

In the centre as the density, mass and weight distribution is constant

Question 17

In an asymmetrical object, where is the centre of gravity located?

Answer 17

The centre of gravity shifts to the area of greater mass

eg baseball bats COG is away from the handle towards the end because that is where most of its weight is

Question 18

Why is it difficult to find the centre of gravity in the human body?

Answer 18

Because of the moving parts and unequal weight distributions

Question 19

How can you find the centre of gravity in the human body?

Answer 19

Segmental

Box Method

Question 20

Segmental

Answer 20

Looks at each segment and determining the centre of gravity for each body segment and then averaging it to find the actual centre of gravity

Question 21

Box Method

Answer 21

Draw a box around a body or object with a cross through it, where the two lines intersect is the centre of gravity

Question 22

Line of Gravity

Answer 22

The direction in which gravity acts on the body is known as the line of gravity

Question 23

How is stability increased - line of gravity

Answer 23

When the line of gravity acts through the centre of the base of support, stability is increased

Question 24

How is stability decreased - line of gravity

Answer 24

When the line of gravity acts outside the centre of the base of support, stability is decreased and disrupted

Question 25

Give an example of how is stability decreased - line of gravity

Answer 25

swimmers use this to their advantage on starting blocks to increase acceleration

Question 26

How can equilibrium be maintained?

Answer 26

When the line of gravity is on the edge of the base of support then equilibrium can be maintained

Question 27

Give an example of how can equilibrium be maintained?

Answer 27

Rugby players will lean forward as they move towards opposition so that their line of gravity has further to move before exiting the Base of Support and disrupting stability

Question 28

Body Mass

Answer 28

The greater the mass of a body or object, the more force is required to move it and thus, disrupt its equilibrium (newton's 2nd law)

Question 29

Friction

Answer 29

Increasing friction between the body and the contact surface, increases the person's stability eg a surfboard with wax (feet on board)

Question 30

How can athletes maximise stability?

Answer 30

Increasing BOS Ensuring the line of gravity is within the BOS Lowering the COG Increasing their mass Increasing friction Expanding their BOS Shifting the line of gravity towards an oncoming force

Question 31

What is a lever?

Answer 31

A simple machine consisting of a rigid bar (bones in the body) that can rotate around an axis (joints in the body) in order to exert a force (muscle contractions in the body) on an object

Question 32

In relation to the levers, the human body...

Answer 32

Is a system of levers that allow movement to occur

Question 33

Classification of Levers

Answer 33

Lever system is designed for speed, range of motion, but not force production

Question 34

What are the components of a lever?

Answer 34

A-axis or pivot point R-resistance or load F-force or effort (muscle contraction in the body)

Question 35

First Class Levers

Answer 35

-Axis is in the middle (FAR) -When muscles work in pairs on opposite sides of a joint axis MA=1, when the axis is centred (causes balanced movements) MA<1, when the axis is near the force (causes an increase in speed and range of motion) MA>1 when the axis is near the resistance (causes a lesser force needed to move the resistance)

Question 36

Give an Example of a First Class Lever

Answer 36

``` See-saw bending neck down force- chin axis-jaw/ear resistance - neck muscles ```

Question 37

Second Class Levers

Answer 37

The resistance in a 2nd class lever is positioned cloer to the axis than the force so the force arm is longer than the resistance arm Beneficial in increasing the force output Useful when a heavier load needs to be moved Larger resistance can be moved with little force

Question 38

Give an Example of a Second Class Lever

Answer 38

Standing on tiptoes axis-ball of foot joint resistance- weight on toes force- heel

Question 39

Third Class Levers

Answer 39

Resistance is generally at the end of the lever The axis of rotation is the joint and the and the force is applied by the contracting muscle Force is closer to the axis rather than resistance Require a greater force to move a given resistance, but a greater range of motion and speed are gained A force larger than the resistance should be applied

Question 40

Give an example of Third Class Levers

Answer 40

Flexion of the elbow axis-elbow joint force-attachment of bicep muscle close to the joint resistance- something being held in the hand eg ball

Question 41

Mechanical Advantage

Answer 41

- ratio of force arm to resistance arm | - relates to the positioning of the axis

Question 42

Mechanical Advantage=

Answer 42

force arm/ resistance arm

Question 43

Force Arm=

Answer 43

distance from the axis to the force

Question 44

Resistance Arm=

Answer 44

distance from the axis to the resistance

Question 45

Mechanical Advantage >1

Answer 45

Then less effort is needed to move a resistance

Question 46

Mechanical Advantage <1

Answer 46

There is an increased range of motion and angular speed

Question 47

Which type of lever is most common in the human body?

Answer 47

3rd class

Question 48

Lever Length

Answer 48

Anatomical levers in the body are often extended through the use of a racquet etc This increases distance from axis to the resistance so the resistance arm is longer than the force arm. A greater force is required which increases the velocity allowing the ball to be hit further

Question 49

How do children benefit from modified sporting equipment that is smaller and lighter?

Answer 49

Longer levers can be more difficult to swing because of the length and greater mass increasing moment of inertia. Modified equipment may be a shorter handle or light weight.