Angular Kinetics PDF

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Lecture notes on angular kinetics (biomechanics module)...

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Biomechanics lecture- angular kinetics Angular kinetics is the study of the causes of rotation, and the changes that occur within rotation. to rotate an object, a force must be applied that is called an off-centre (eccentric) force, this causes translation of an object and rotation. Applying a force through the centre of mass causes translation only. To obtain rotation only, a couple is required. A couple is a pair of equal and opposite forces whose line of action (direction of force) are not aligned. Torque Torque is the turning effect of an object (how much it rotates). This depends on:  

The size of the force How far the force is from the axis of rotation

Equation for torque= T=F x D F= force, D= distance from the forces line of action to the axis of rotation. Torque is measured Newton Metres Moment of inertia Moment of inertia is a measure of how hard it is to angularly accelerate or decelerate an object. Moment of inertia is the equivalent of mass in an angular setting Moment of inertia depends on:  

The mass of an object How that mass is distributed eg a non-rigid object, like humans, can change their moments of inertia

Humans can change their moments of inertia by changing our posture Angular momentum Angular momentum is a measure of how much rotation an object has. depends on the object’s moment of inertia and angular velocity. Formula= H= I x W (I= moment of inertia, W= angular velocity) 1st law of angular momentum= Conservation of Angular Momentum= In the absence of a net external torque, an object’s angular momentum stays unchanged 2nd law of angular momentum= when an object is receiving a net external torque, its angular acceleration is: A= T/I (A= acceleration, T= Torque, I= Moment of Inertia) 3rd law of angular momentum= Every torque has an equal and opposite reaction torque angular momentum is constant in the air (divers, gymnasts, trampolinists etc) and selected other activities (figure skaters etc). An athlete can use changes in their moment of inertia to control their speed of rotation...