Balance, stability and Equilibrium (Unit 3 AOS 1 Terms)

Question 1

Balance def

Answer 1

the ability to maintain control and equilibrium

The ability to control equilibrium

Question 2

stability def

Answer 2

Having a high degree of equilibrium and being able to resist changes to that state. Ability to ‘return to desired position or trajectory following a disturbance to equilibrium’

The resistance to disruption of equilibrium

Question 3

Equilibrium def

Answer 3

A state in which opposing forces are balanced. State of no acceleration meaning not changing speed or direction. Either static (without movement) or dynamic (moving with constant velocity).

Question 4

when is an object in a stage of equilibrium

Answer 4

An object is in equilibrium when there are no unbalanced forces or torques acting upon it.

Question 5

2 types of equilibrium

Answer 5

Static equilibrium: The body or object must not be moving or rotating. The sum of all the forces acting on the body is 0. (MOTIONLESS)

Dynamic equilibrium: The state in which the body or an object is moving with a constant velocity. (More important in a sporting context)

Question 6

Factors affecting stability

Answer 6

Base of support
Centre of gravity
Line of gravity

Question 7

Base of Support

Factors affecting stability

Answer 7

The larger the base of support, the greater the stability of the object.

The base of support is bound by the outside edges of the body parts in contact with the surface

+++base of support is anything in contact with the surface+++
eg: surfboard
beam in gymnastics

Question 8

Centre of gravity (AKA Centre of mass)

Answer 8

The theoretical point in an object at which its entire mass appears to be concentrated.

Generally it is close to the belly button but is moved by moving body parts.

The lower the centre of gravity, the more stable the body will be.

Question 9

List 3 sporting examples where lowering the centre of gravity increases stability

Answer 9

skiing
gymnastics - lowering COG by bending the knees in gymnastics allows an individual to land in a stable position and also impulse can be applied to this by increasing the time over which the force is applied to limit injury

surfing - widen our base of support and bend knees by lowering COG to increase stability

Question 10

Line of gravity

Answer 10

Gravity acts on a body through the centre of gravity. The direction in which the gravity acts is called the line of gravity.

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

Movement can only occur when the line of gravity falls outside the objects base of support

Question 11

When is it an advantage for the line of gravity to fall outside the objectsbase of support

Answer 11

the individual is les stable allowing them to have a faster start

Question 12

How can athletes maximise stability?

Enhancing equilibrium, maximising stability and achieving balance

Answer 12

Increasing the size of the base of support
Ensure the line of gravity falls within the base of support
Lower the centre of gravity
Increase the body’s mass
Increase friction between the body and the surface
Extend the base of support in the direction of the oncoming force
Move the line of gravity towards the oncoming force

Question 13

Levers

Answer 13

A lever is a simple machine consisting of a rigid bar that can be made to rotate around an axis in order to increase FORCE and/or SPEED

A lever system can be used to either multiply force and move a heavy resistance more easily or to produce range of motion and multiply speed.

in body:
- rigid bars are bones
- axis are joints

Question 14

the three parts of levers

Answer 14

1. Axis (pivot point) - fulcrum in other pieces
   eg in body: the fixed joint/axis in the body that the lever moves around
2. Resistance (weight or load to be moved)
   eg in body: the bone of the body and whatever is being held or moved by the bone.
   could be ball, bosy or bat etc
3. Force (effort)
   eg in body: the muscles that contract to generate the force to move the lever

ARF - acronym - its all about whats in the middle

force in the body are generally muscles

Question 15

Types of levers

Answer 15

First class lever: The resistance and the force are on either side of the axis.
RAF

Second class lever: The resistance is between the force and the axis.
FRA

Third class lever: The force is between the resistance and the axis.
RFA

Question 16

First class levers

Answer 16

Designed for FORCE

RAF

Body example: nodding head forward and backwards. Limited examples in the human body

Question 17

2nd class lever

what are they for and example\e

Answer 17

Help move a heavy load with FORCE

FRA

Body example:
Up phase of push up

up phase on tip does (resistance is body mass, axis is toes and force is calf (gastrocnemius and soleus) muscle pulling

down phase on sit up - look at slide 25 on ‘balance, stability and equilibrium’ powerpoint

Question 18

Third class lever

Answer 18

• most common types of lever in the human body

RFA

These levers have a longer resistance arm than force arm and therefore have a mechanical disadvantage, but the lever has the ability to produce greater speed.

Eg. throw, hit, kick

Question 19

The 2 ways levers provide a mechanical advantage

Answer 19

Allow for a small force to move a large resistance

Eg:
bottle opener, wheelbarrow, crow bar
To generate speed by moving one point of an object a small distance which causes another part to move a relatively large distance.
Example: Racquets and bats

Question 20

The mechanical advantage of levers (formula)

Answer 20

Mechanical advantage:
Force arm/ resistance arm

Question 21

mechanical advantages of levers (if force arm length is greater than resistance arm length)

Answer 21

if force arm is greater than 1, force arm is longer than resistance arm therefore the action will provide more force

• mechanical advantage of greater than one

+++All second-class levers.+++

The force required to move the load is less than the force of the resistance. That is, greater weight can be moved with less effort.

Smaller range of motion achieved.

large resistance can be moved with relatively small force

Question 22

mechanical advantages of levers (if resistance arm length is greater than force arm length)

Answer 22

if force arm is less than one, resistance arm is longer than force arm therfore the action will produce more speed

• mechanical advantage of less than 1

+++All third-class levers+++

There is an increased range of motion and speed.

more force is required to move a relatively small resistance but the lever has the ability to produce greater speed.

increase speed and ROM ???what is ROM???

Greater force needs to be applied but it only needs to be applied over a smaller distance. (you need to be able to provide enough force)

requires large force to move a relatively small resistance

Question 23

mechanical advantages of levers (if force arm length is the same as resistance arm length)

Answer 23

1= lever is balanced between force and speed (Force arm and resistance arm equal)

Question 24

Summation of momentum and levers

Answer 24

When multiple levers work together, they produce the most power

Question 25

Lever length and velocity

Answer 25

The velocity is greater at the end of a long lever than at the end of a short lever

The further a point of a lever is from the axis then the greater its velocity.

Question 26

eg on how to structure response for levers (Using a handball, perform a throw)

Answer 26

Using a handball, perform a throw

answer:
An overarm throw involves a third class lever as the resistance arm (the distance between the shoulder and the handball) is longer than the force arm (the distance between the shoulder and the insertion point of the bicep). This creates the mechanical advantage to become less than one. This therefore increases the speed of the throw, allowing the handball to travel a furhter distance.

Question 27

how to structure a response for levers (complete a tennis serve off a short racquet vs longer raquet

Answer 27

A tennis serve involves a third class lever. This is because the force (bicep) is located in between the axis (shoulder joint) and the resistance (the ball). Due to the force arm (the distance between the shoulder and the insertin point of the bicep) is shorter than th resistance arm (the distance between the shoulder and the ball), there is a mechanical advantage of less than one. This means the angular vfelocrty of the raquet increases, therefore the speed and distance of the ball will increase

By using a longer racquet, this same arm is extended therefore, the angular velocity is increased even more, further increasing the speed and distance the ball will travel

Question 28

why do children use smaller bats

Answer 28

The child cannot overcome the moment of inertia of a large tennis racquet