torque and rotation

how might you apply a force to ensure it goes in a straight line only

apply the force at the center of mass

what happens if force applied but is not applied to the center of mass

the center of mass is accelerated and the body rotates

force times the perpendicular distance from the center of mass is

torque applied (moment of force)

Perpendicular distance

moment arm/lever arm

when the athlete is in the air point of rotation will be

the point of rotation is the center of mass

rotation and torque acts about

the joint

calculation of torque (moment of force)

Angular acceleration that resultes from torque calculatoin

where I is the moment of inertia

and alpha is the angular acceleration

Moment of Inertia (rotational mass)

mr²

torque is a

vector

torque magnitude calc

Torque characteristics

1. Magnitude is

2. the direction is along the axis of rotation

3. point of application is the center of the joint

4. line of action is along the axis of rotation

each body segment has its

own center of mass, gravity works downwards at each of these segmental centers of mass

overall center of mass

The position on the body where the torques created by each segment’s gravity are all balance

when torques are balanced what happens to rotation

no rotation occurs

when torques are not balanced what happens to rotation

rotation occurs

why are pushups on your knees easier

• shortening the moment arm for your body weight so it producews less torques about the axis

• less force required from arms