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Statics

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Statics

- There are three conditions for static equilibrium.
- The object is at rest
- There is no net force
- There is no net torque

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

F

-F

With no rotation, torques must sum to zero.

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

FNW

FNF = mg

Ffrmmg

-mg

q

The calculation of torques is independent of the pivot point.

Select the wall for the pivot.

FNW

FNF = mg

Ffrmmg

-mg

q

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.

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

- 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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