Stability and Angular Motion Flashcards
Define the term angular motion
When a body or part of a body moves in a circle or part of a circle about a point (axis of rotation)
What is centre of mass?
The point at which the body is balanced in all
Directions
Define the term stability
The ability of a body to return to equilibrium or its original position after being displaced
A more stable body is harder to move
Describe 4 ways to maximise stability
Lower centre of mass
Increase size of base of support
Make line of gravity central to base of support
Increase body mass or inertia
What is a fulcrum?
A fixed point of rotation about which the lever moves
E.g - joint
What is the effort in a lever system?
The force being applied that causes the lever to move
E.g muscle
What is stability?
the ability of a body to return to equilibrium after being displaced
What is equilibrium?
a body is in equilibrium when the net force is 0 (all forces are equally balanced)
What is the centre of mass?
the point at which the body is balanced in all directions
Identify the factors that affect stability
height of centre of mass
size of base of support
line of gravity in relation to base of support
body mass or inertia
how does height of centre of mass affect stability?
the lower the centre of mass, the greater the stability
how does size of base of support affect stability?
the greater (wider, or more points in contact with the floor) the base of support, the greater the stability
how does the line of gravity in relation to base of support affect stability?
if the line of gravity is central to the base of support, stability is greate
how does mass / or inertia affect stability?
the greater your mass / inertia, the greater your stability as more force is required to move you
In a lever system in the body, what acts as a fulcrum?
a joint
In a lever system in the body, what acts as a load?
the weight to be moved (body part or object)
In a lever system in the body, what acts as the effort?
muscles
What is in the middle of a first class lever?
fulcrum
What is in the middle of a second class lever?
load
What is in the middle of a third class lever?
effort
Give an example if a first class lever in the body
neck extension
E = trapezius
F = joint between atlas and skull
L = weight of head
Give an example of a second class lever in the body
elbow in an overarm throw
F = elbow joint
L = weight of lower arm and ball in hand
E = triceps muscle
Give an example of a third class lever in the body
standing on tiptoes when jumping up
F = joints between metatarsals and phalanges
E = gastrocnemius
L = weight of body
What is a load arm?
the perpendicular distance of the load fro the fulcrum
What is an effort arm?
the perpendicular distance from the effort to the fulcrum
What is meant by the term ‘mechanical advantage’?
if you have a mechanical advantage it means that the lever system can move a large load with a relatively small effort. It occurs in a 2nd class lever system where the effort arm is greater than the load arm
What is meant by the term ‘mechanical disadvantage’?
Mechanical disadvantage means that the effort would need to be considerably bigger than the load in order to move the load. It occurs in a third-class lever system where the load arm is greater than the effort arm
What is moment of force / torque?
the effectiveness of a force to produce rotation about an axis.
Moment of force = force x perpendicular distance from fulcrum (Nm)
the bigger the force or further away it is from the axis, the bigger the moment of force
Longer effort arm = greater acceleration (mechanical advantage)
What is an axis of rotation?
an imaginary line or point about which the body or part of the body rotates
where is the longitudinal axis?
it runs top to bottom passing through the centre of mass
a pirouette would turn about this axis
Where is the transverse axis?
it runs left to right passing through the centre of mass
a somersault would turn about this axis
Where is the frontal axis
it runs front to back, passing through the centre of mass
a cartwheel turns about this axis
What is a radian?
the unit of measurement for angular distance and angular displacement
1 rad = 57.3 degrees (roughly)
Describe the angular analogue or Newton’s 1st Law
Inertia - a body at rest will not rotate unless a force is acted upon it. A rotating body continues to turn about its axis with constant angular momentum unless acted upon by an external force
what is angular distance?
the angle through which the body has rotated about its axis (rad)
what is angular displacement?
the shortest change in angular position from start to finish (rad)
what is angular speed?
the angular distance travelled in a certain time (rad/s)
what is angular velocity?
the angular displacement travelled in a certain time (rad/s)
what is angular acceleration?
the rate of change of angular velocity (rad/s/s)
change in angular velocity / time taken
What is angular momentum?
the quantity of angular motion possessed by a rotating body.
angular momentum = moment of inertia x angular velocity
what is moment of inertia?
the resistance of a rotating body to change its state of angular motion
What factors affect moment of inertia?
- mass of body
- distribution of mass from axis of rotation
How does mass affect moment of inertia?
the bigger the mass, the greater the moment of inertia (e.g. the bigger you are, the more torque (force) you need to move you)
How does distribution of mass from axis of rotation affect moment of inertia?
the further the distribution of mass from the axis of rotation, the greater the moment of inertia (e.g. the more spread out your arms and legs, the more torque (force) you need to turn)
