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# Statics - PowerPoint PPT Presentation

Statics. Static Equilibrium. There are three conditions for static equilibrium. The object is at rest There is no net force There is no net torque. With no motion, forces must sum to zero. Each component is treated separately. Find the tension in the ropes. T is the tension to the left

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## PowerPoint Slideshow about ' Statics' - connley-bogue

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Presentation Transcript

### Statics

• There are three conditions for static equilibrium.

• The object is at rest

• There is no net force

• There is no net torque

Each 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 sinq = W = mg

T = mg / sinq = 3.9 x 103 N

Horizontal equality

S = T cosq = 3.4 x 103 N

Static Forces

q = 30º

m = 200 kg

• Balanced forces do not insure static equilibrium.

• The center of mass is stationary, but the object rotates.

F

-F

A ladder leans against a wall with friction against the floor.

Length l

Angle q

Coefficient of static friction m

The sum of torques gives

Static Torques

FNW

FNF = mg

Ffrmmg

-mg

q

Select the wall for the pivot.

Pivot Point

FNW

FNF = mg

Ffrmmg

-mg

q

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.

The Lever

Human Lever point.

• The elbow joint is a pivot point for a lever.

• Assume all forces are vertical.

• Levers may not reduce force.

Stability point.

• When is an object in static equilibrium?

• Check the forces and torques

• If the torques are from gravity, find the center of mass

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