angular motion Flashcards
angular motion
angular motion is movement of a body or part of a body in a circular path about an axis of rotation
example of angular motion
- a gymnasts whole body will rotate around the high bar (axis of rotation)
- an athletes legs rotate at the hip point (axis of rotation) as they run
- a trampolinist whole body rotates around their centre of mass during a somersault
what does angular motion result from
- angular motion results from an eccentric force being applied to a body the force is applied outside the centre of a body’s mass
- an eccentric force is also known as torque
eccentric force
a force applied outside the centre of mass, resulting in angular motion
torque
a measure of the turning (rotational or eccentric) force applied to a body
what is an axis of rotation?
an imaginary line that passes through the centre of mass about which a body rotates: longitudinal, transverse and sagittal axis
what is the longitudinal axis?
axis that runs from head to toe through the centre of mass
what is the transverse axis?
transverse axis runs from the left to right through the centre of mass
what is the saggital axis?
frontal axis runs from front to back through the centre of mass
what is angular motion measured in?
radian (rad)
what is radian (rad)
- a unit of measurement of the angle through which a body rotates
- 360 degrees = 2 pi radians, 1 radian = 57.3 degrees
angular velocity
angular velocity is the rate of change in angular displacement or simply the rate of rotation
equation for angular velocity
angular velocity = angular displacement/time taken
practical example of angular velocity
- a trampolinist performing a seat drop rotates their legs clockwise about the transverse axis 1.57 radians in 0.5 seconds
- the average angular velocity is 3.14rad/s (1.57rad/0.5s)
equation for moment of inertia
sum of(mass x distribution of the mass from the axis of rotation squared)
units for moment of inertia
measured in kilogram metres squared (kgm squared), mass in kilograms and distribution of the mass from the axis of rotation in metres squared
what is moment of inertia?
- is the resistance of a body to change its state of angular motion or rotation
- 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 momentum; it will resist increasing or decreasing the rate of spin
- moment of inertia is the angular or rotational equivalent of inertia
two factors that affect the moment of inertia are what?
- mass
- distribution of mass
explain how moment of inertia has a direct effect on angular velocity
- if moment of inertia is high, resistance to rotation is also high, therefore angular velocity is low: the rate of spin is low
- if 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?
- is the quantity of angular motion possessed by a body
- it is the rotational equivalent of momentum
equation for angular momentum
angular momentum = moment of inertia x angular velocity
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
