Statics

Static Equilibrium  There are three conditions for static equilibrium. 1.The object is at rest 2.There is no net force 3.There is no net torque

Static Forces  With no motion, forces must sum to zero. Each component is treated separatelyEach component is treated separately  Find the tension in the ropes. T is the tension to the left S is the tension to the right W is the weight downward  Vertical equality T sin  = W = mg T = mg / sin  = 3.9 x 10 3 N  Horizontal equality S = T cos  = 3.4 x 10 3 N m = 200 kg  = 30º

Offset Forces  Balanced forces do not insure static equilibrium.  The center of mass is stationary, but the object rotates. F -F

Static Torques  With no rotation, torques must sum to zero.  A ladder leans against a wall with friction against the floor. Length l Angle  Coefficient of static friction   The sum of torques gives -mg F NW F NF = mg F fr   mg 

Pivot Point  The calculation of torques is independent of the pivot point.  Select the wall for the pivot. -mg F NW F NF = mg F fr   mg 

The Lever  The lever is a simple machine that increases force.  The downward force is multiplied by the lever arm of the stick to become a torque.  The torque on the rock matches the torque from the person.

Human Lever  The elbow joint is a pivot point for a lever. Assume all forces are vertical. Levers may not reduce force.

Stability  When is an object in static equilibrium? Check the forces and torquesCheck the forces and torques If the torques are from gravity, find the center of massIf the torques are from gravity, find the center of mass next