Biomechanics - angular motion Flashcards
What is the definition of angular motion
movement of a body or part of a body in a circular path about an axis of rotation
eg of angular rotation
a gymnast whole body will rotate will rotate around a bar (axis of rotation)
What is an eccentric force
a force applied outside the centre of mass, resulting in angular motion
What is torque
A measure of the turning (rotational or eccentric) force applied to the body
What does angular motion result from
an eccentric force being applied to a body where the force is applied outside the centre of a body’s mass
What is the principal axis of rotation
an imaginary line that passes through the centre of mass about which a body rotates: longitudinal, transverse and frontal axis
What is the longitudinal axis of rotation
From head to toe through the centre of mass
A body rotating around the longitudinal axis would be performing actions such as a flat spin on the ice or full turn in trampolining
What is the transverse axis of rotation
left to right through centre of mass
a body rotating around the transverse axis would be performing actions such as sommersults
What is the frontal axis of rotation
front to back through the centre of mass
a body rotating around the frontal axis be performing actions such as cartwheels
3 key descriptors important for angular motion
1- angular velocity
2- movement of inertia
3-angular momentum
What is angular motion measured in
radians
What is a radian
a unit of measurement of the angle through which a body rotates.
Calculation of angular velocity
angular displacement
/
time taken
What is angular velocity
the rate of change in angular displacement measured in radians per second (rate of spin)
How is angular velocity measured
in radians per second (rad/s)
What is moment of inertia
the resistance of a body to change its state of angular motion or ration
A resting body will not want to start rotating around an axis and
a rotating body will not want to change its angular motion or movement
it will resist increasing or decreasing the rate of spin
How can moment of inertia be calculated
sum of (mass x distributution of the mass from the axis of rotation)
How is moment of inertia measured
kgm2
Two factors that affect moment of inertia
mass- greater mass= greater moment of inertia
and
distribution of mass from axis of rotation- further mass moves from axis of rotation = greater movement of inertia
If moment of inertia is high - what is the resistance to rotation and angular velocity and rate of spin
resistance to rotation- high
angular velocity is low
rate of spin - slow
If moment of inertia is low - what is the resistance to rotation and angular velocity and rate of spin
resistance to rotation- low
angular velocity- high
rate of spin- fast
How would an ice skater manipulate their body to reduce moment of inertia
bringing arms and legs closer to midline ot body) = rotate quicker
How would an ice skater manipulate their body to increase moment of inertia
moving limbs away from midline of the body
reduces angular velocity and decreases rate of spin
What is angular momentum
the quantity of angular motion possessed by a body
equation for angular momentum
moment of inertia
x
angular velocity
What is angular momentum measured
kgm2rad/s
To start rotating around an axis what must be generated in the preparation/ take off phase of rotational movement?
and what must be applied
momentum
eccentric force or torque must be applied
How does a high-board diver create rotation
jump away from the board
they lean away from board at take off so the reaction force generated from the diving board passes outside their centre of mass
(they lean back to create a spinning effect)
this creates an eccentric force applied to the body, the greater the quantity of angular momentum generated for the movement
Extend your knowledge-
Newtons laws of motion have angular ‘versions’ known as…….
analougues
What is the analogue of newtons second law of motion
‘the rate of change in angular momentum of a body is directly proportional to the size of the eccentric force (torque) applied
and takes place in the same direction as the eccentric force is applied
Extend your knowledge
Linking to a diver- what will a greater eccentric force applied to the diver at take off from the board lead to
the greater the rate of change in angular momentum generated
What is conservation of angular momentum
angular momentum is a conserved quantity which remains constant unless an external eccentric force or torque is applied
What is angular analogue of newtons first law of motion
the angular equivalent of newtons first law of motion
- which states a rotating body will continue to turn about its axis of rotation with constant angular momentum
unless acted upon by an eccentric force or external torque
A moment of inertia increases, angular velocity …………..
decreases
Once angular momentum is generated does it change throughout movement
no it remains constant
known as a conserved quantity
means performer can continue rotating for a long period of time
Key descriptors of angular motion
movement of inertia, angular velocity and angular momentum.
