Angular Motion

• Angular motion: movement of a body (or part of a body) in a circular path about an axis of rotation, e.g. bending your arm in a tennis serve.
• To create angular motion an eccentric force must be applied to the body.
• An eccentric force is an external force that is applied off the centre of mass.
• Either the centre of mass or the joint on the highbar becomes the axis of rotation.
• Torque us a measure of the turning force applied to a body.
• Torque is often referred to as the moment of force.
• Moment of force = force x distance
• Moment of force / torque is measured in newton metres (Nm).
• Moment of force is described as the effectiveness of a force to create rotation about an axis.
• You can measure the moment of force/torque required to move a body around an axis or create a turning force.
• An axis is an imaginary straight line around which a body or part of a body rotates.
• Movement at a joint takes place in a plane around an axis.
• There are three axes of rotation: transverse axis, longitudinal axis, and frontal axis.
• The transverse axis passes horizontally from left to right.
• Movements about the transverse axis include a somersault and flexion and extension at the elbow.
• The longitudinal axis is also known as the vertical axis and passes vertically from the bottom to the top.
• Movements about the longitudinal axis include rotation.
• The frontal axis passes horizontally from back to front.
• Movements about the frontal axis include abduction and adduction.
• A radian is a unit of measurement of the angle through which a body rotates.
• 360º = 2π
• Angular distance is the total angle a body turns through from start to finish position when rotating about an axis.
• Angular displacement is the smallest angle between the start and finish position of a body rotating about an axis.
• Angular speed is the rate of change in angular distance.
• Angular speed = angular distance/ time taken.
• Angular speed is measured in rads/s^1.
• Angular acceleration is the rate of change in angular velocity.
• Angular velocity = final angular velocity - initial angular velocity / time taken
• Angular acceleration is measure in rads/s^2
• Moment of inertia is the resistance of a body to change its state of angular motion.
• Moment of inertia is the rotational equivalent of inertia.
• Moment of inertia = sum of (mass x distribution of the mass from the axis of rotation).
• Moment of inertia is measured in kilograms metres^2 (kgm^2).
• MI = 𝛴m x r2
• Angular velocity is the rate of change in angular displacement or the rate of rotation.
• Angular velocity = angular displacement / time taken.
• Angular velocity is measured in rads/s.
• Angular momentum is the quantity of angular motion posessed by a body.
• Angular momentum is the rotational equivalent of momentum.
• Angular momentum = moment of inertia x angular velocity.