Angular motion Flashcards
Angular motion
The motion of a body about a fixed point or axis, causing rotation or spin.
e.g.
> a gymnast or diver somersaulting
> athletes legs at the hip as they run
3 Principles of angular motion
Angular momentum-
Angular velocity x moment of inertia
Angular momentum
Rotational force of the object.
(speed of rotation)
Angular velocity
Speed of rotation.
Moment of inertia
Object’s resistance to movement.
Conservation of momentum
No external torque acts on the body, so the angular momentum of a rotating body remains constant.
Angular displacement
The distance, in a revolution, from a start to finish point.
Angular velocity
Angular velocity -
Angular displacement/time
Angular acceleration
Angular acceleration -
(Final angular velocity - Initial angular velocity)/time
Units
Radians, rad/s, rad/s^2
2 factors affecting moment of inertia
1) Mass
2) Distribution of mass from the axis of rotation
Mass
> The greater the mass, the greater the moment of inertia
Low mass (gymnasts, divers) can start, change rate of, and stop rotation with relative ease
Distribution of mass from the axis of rotation
> The further the mass is from the axis of rotation, the greater the moment of inertia
Tucked front somersaults rotate quicker than straight
Increasing rotations (diving)
> Arms and legs tucked in
Decreases distribution of mass from the axis of rotation
Decreasing moment of inertia
Increasing angular velocity
Increasing rotations
Decreasing rotations (diving)
> Body straightens
Increases distribution of mass from the axis of rotation
Increasing moment of inertia
Decreasing angular velocity
Decreasing rotation
Over rotation (trampolinist)
BASED ON CONSERVATION OF MOMENTUM:
> Athletes limbs are too close to centre of mass (or for too long)
> Distribution of mass is closer to the axis of rotation
> Decreased moment of inertia
> Increased angular velocity
> Increasing rotation - over rotation
Under rotation (trampolinist)
BASED ON CONSERVATION OF MOMENTUM:
> Athletes limbs are too open (or open out too early)
> Distribution of mass is further from the axis of rotation
> Increased moment of inertia
> Decreased angular velocity
>Decreased rotation - under rotation
