Joint Kinetics

law of inertia/equilibrium

for an object to be in equilibrium, the sum of all the forces and the sum of all the moments/torque applied to that object must be zero

static

study of condition under which objects remain at rest or moves at a constant velocity(a=0, net force=0)

1st law

Dynamics

study of motion of objects under the action of forces

a and net force don’t equal 0

2nd law

how to increase acceleration

smaller mass

a larger net force

Moment of inertia

mass property(I) that determines the torque needed for a desired angular acceleration(alpha) about an axis of rotation

I = sum of (mass*radius squared)

pounds to newtons

1 lb = 4.45

free body diagram

stick figure drawing of the system being analyzed on which vectors representations of the forces and/or moments acting on the system are indicated

Effects of forces

tension/traction

compression

shear

tension/traction

application of outward/pulling forces

compression

application of inward/pushing forces

shear

application of forces parallel to the application surface

in the direction of movement

creates the torque

effects of muscle force on joints

compression - approximation

traction - distraction