Angular Motion Flashcards
What is angular motion?
Movement of a body or part of a body in a circular path about an axis is rotation.
What type of force is required to create angular motion?
Eccentric force
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/eccentric force applied to a body
Name the 3 axis of rotation
Frontal
Transverse
Longitudinal
Where does the longitudinal axis run through?
Runs from the head to the toe through the centre of mass
Where does the transverse axis run through?
Runs from the left to right through the centre of mass
Where does the longitudinal axis run through?
Runs from front to back through the centre of mass
Which movements can occur around the longitudinal axis?
Give 2 examples of sporting actions that turn about the longitudinal axis
Rotation, medial and lateral rotation
Pirouette in ballet / Full twist in trampolining
Turning head to breath in front crawl
Which movements can occur around the transverse axis?
Give 2 examples of sporting actions that turn about the transverse axis
Flexion and Extension, dorsiflexion and plantar flexion
Bicep curl
Somersault
Which movements can occur around the frontal axis?
Give 2 examples of sporting actions that occur about the frontal axis.
Abduction and adduction
Star jump
Cartwheel
What is angular velocity?
The rate of change in angular displacement
What is angular velocity measured in?
Radians per second
How do you calculate angular velocity?
Angular velocity = angular displacement / time taken
What is moment of inertia?
The resistance of a body to change its state of angular motion or rotation
How do you calculate moment of inertia?
MOI = mass x distribution of mass from the axis of rotation
What is moment of inertia measured in?
kgm squared
What two factors effect moment of inertia?
Mass
Distribution of mass from the axis of rotation
How does mass effect moment of inertia?
The greater the mass of the body the greater the MOI
How does distribution of mass from the axis of rotation affect moment of inertia?
The greater the distribution of mass from the axis of rotation, the greater the MOI
Explain how moment of inertia has a direct effect on angular velocity
- If the moment of inertia is high, resistance to rotation is also high, therefore angular velocity is low: the rate of spin in slow
- If the moment of inertia is low, resistance to rotation is also low, therefore angular velocity is high: the rate of spin is fast
What is angular momentum?
The quantity of angular motion possessed by a body
How do you calculate angular momentum?
Angular momentum = moment of inertia x angular velocity
What is angular momentum measured in?
Kgm(squared)rad/s
What is meant by the term conservation of angular momentum?
Angular momentum is a conserved quantity that remains constant unless an external eccentric force is applied
Describe the angular analogue of Newtons 1st law of motion
A rotating body will continue to turn about its axis of rotation with constant angular momentum unless acted on by an eccentric force.
Explain how conservation of angular momentum would be applied for an ice skater doing a triple axel jump
- At the start of the jump, the ice skater applies an eccentric force to begin rotation around the longitudinal axis.
-Initially their MOI is high as their arms and legs are spread out, taking their distribution of mass away from the axis of rotation. During this point their angular velocity is low.
-They then bring their arms and legs close to the longitudinal axis, this decreases MOI and increases angular velocity.
-When they want to slow down, the ice skater takes their arms and legs back out to the sides to once again take their distribution of mass away from the axis of rotation. This increases their MOI, which decreases their angular velocity.
-During this, angular momentum stays the same, as angular velocity and MOI are inversely proportional, when one increases the other decreases, to keep angular momentum constant.
