angular motion

what is angular motion

rotation around a fixed point or axis

can be whole body e.g. somersault or part of a body e.g. arms throwing a discus

occurs when an eccentric force is applied outside the centre of mass

what axis do figure skaters rotate on

longitudinal axis

what axis do gymnasts flip on

transverse axis

what is torque

turning force

• angular motion occurs as a result of torque

• it causes an object to turn around its axis of rotation

• increasing the eccentric force increases the torque

what is the equation for torque

torque (nm) = force (n) x perpendicular distance (m)

what is newtons first law of angular motion and give an example

a rotating body will continue to turn about its axis of rotation with constant angular momentum unless an external torque is exerted upon the body

e.g. a gymnast will keep rotating around their axis of rotation until they hit the floor (external torque)

what is newtons second law of angular motion and give an example

the rate of change of angular momentum is proportional to the torque causing it and the change that takes place in the direction in which the torque acts

e.g. a gymnast who wants to flip faster will apply a larger force in the direction they want to flip

what is newtons third law of angular motion and give an example

when a torque is applied by one body to another, the second body will exert an equal and opposite torque on the other body

e.g. when a goalkeeper saves the ball and their arms reach behind them, their legs to back

define moment of inertia

the resistance of a body to angular motion (rotation)

what can moment of inertia be affected by

mass of the body/object

distribution of mass from the axis of rotation

how does the mass of a body affect inertia

the greater the mass, the greater the inertia

e.g. football and bowling ball

how does the distribution of mass from the axis of rotation affect inertia

the closer the distribution of mass is from the axis of rotation, the lower the inertia, making it easier to turn

the further away the distribution of mass is from the axis of rotation, the higher the inertia, making it harder to turn

what is the equation for angular momentum

moment of inertia x angular velocity

what is angular momentum

the quantity of rotation a body possesses

it’s a constant

what is angular velocity

spin speed

what is angular displacement

the smallest change in angle between the starting point and finish point

measured in degrees and radians

how many degrees is 1 radian

57.3 degrees

what is the equation for angular velocity

angular velocity (rad/s) = angular displacement (rad) / time taken (s)

what is angular acceleration

the rate of change of angular velocity

what is the equation for angular acceleration

angular acceleration = change in angular velocity / time taken (s)

what is the relationship between moment of inertia and angular velocity

• moment of inertia increases as distribution of mass from axis of rotation increases

e.g. if arms and legs spread out

• this causes angular velocity to decrease so the performer spins slower

• moment of inertia decreases if distribution of mass is closer to the axis of rotation

e.g. arms and legs tucked in

• this causes angular velocity to increase so the performer spins faster, so is more likely to win