Balance, stability and Equilibrium (Unit 3 AOS 1 Terms) Flashcards
Balance def
the ability to maintain control and equilibrium
The ability to control equilibrium
stability def
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
Equilibrium def
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).
when is an object in a stage of equilibrium
An object is in equilibrium when there are no unbalanced forces or torques acting upon it.
2 types of equilibrium
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)
Factors affecting stability
Base of support
Centre of gravity
Line of gravity
Base of Support
Factors affecting stability
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
Centre of gravity (AKA Centre of mass)
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.
List 3 sporting examples where lowering the centre of gravity increases stability
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
Line of gravity
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
When is it an advantage for the line of gravity to fall outside the objectsbase of support
the individual is les stable allowing them to have a faster start
How can athletes maximise stability?
Enhancing equilibrium, maximising stability and achieving balance
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
Levers
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
the three parts of levers
- Axis (pivot point) - fulcrum in other pieces
eg in body: the fixed joint/axis in the body that the lever moves around - 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 - 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
Types of levers
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
First class levers
Designed for FORCE
RAF
Body example: nodding head forward and backwards. Limited examples in the human body
2nd class lever
what are they for and example\e
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
Third class lever
- 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
The 2 ways levers provide a mechanical advantage
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
The mechanical advantage of levers (formula)
Mechanical advantage:
Force arm/ resistance arm
mechanical advantages of levers (if force arm length is greater than resistance arm length)
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
mechanical advantages of levers (if resistance arm length is greater than force arm length)
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
mechanical advantages of levers (if force arm length is the same as resistance arm length)
1= lever is balanced between force and speed (Force arm and resistance arm equal)
Summation of momentum and levers
When multiple levers work together, they produce the most power
Lever length and velocity
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.
eg on how to structure response for levers (Using a handball, perform a throw)
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.
how to structure a response for levers (complete a tennis serve off a short racquet vs longer raquet
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
why do children use smaller bats
The child cannot overcome the moment of inertia of a large tennis racquet
