Angular motion

define angular motion

movement of body in circular path about axis of rotation

how is angular motion produced

applying an eccentric force outside COM

define torque

measure of turning force applied to body

describe + give an example of each axis of rotation

longitudinal - top to bottom, e.g. pirouette in ballet

transverse - side to side, e.g. front somersault in diving

frontal - front to back, e.g. cartwheel in gymnastics

define + give calculation + units of measurement for moment of inertia, angular velocity + angular momentum

moment of inertia (MI) - resistance of body to change its angular motion/rotation, moment of inertia (kgm²) = ∑ (mass (kg) x distribution of mass from axis of rotation (m²) )

angular velocity - rate of change in angular displacement/rate of rotation, angular velocity (rad/s) = angular displacement (rad) / time taken (s)

angular momentum - quantity of angular motion possessed by a body, angular momentum (kgm²/s) = moment of inertia (kgm²) x angular velocity (rad/s)

describe the factors affecting moment of inertia

mass - greater mass = greater MI

distribution of mass from axis point - further mass from axis point = greater MI

describe the effect of MI on angular velocity

if MI is high resistance to rotation is high so angular velocity is low

define the angular analogue of Newton’s first law of motion

a rotating body will continue to turn about an axis of rotation with constant angular momentum unless acted upon by an eccentric force

explain the conservation of angular momentum

if MI increases then angular velocity decreases + vice versa

so angular momentum does not change once generated

explain how a figure skater manipulates MI when spinning

at start of spin, eccentric force applied into ice to generate angular momentum

swings leg out to change distribution of mass + leans forward to move COM

rotates around longitudinal axis

distribution of mass far from axis point

MI is high so angular velocity is low

during the spin arm are tucked into chest + legs together

brings mass closer to axis point

MI low so angular velocity high

after spin legs + arm move outwards

trying to land with stability

MI increases so angular velocity decreases

friction with ice stops rotation