Pulley

Table Of Contents

Pulley

Machines to change the direction of a force. You can pull things up by pulling with a sideways force.

Mechanical Advantage

A pulley is a simple machine. It reduces the work required to move an object. A 2 Time mechanical advantage shown as below Force would be halved. However, distance increases. Since Work is the same, but force is half, then distance must be doubled.

Assumptions

Rope

• Massless rope
• Frictionless rope. You actually want more friction in real ropes
• Does not stretch

Pulleys

• Massless
• Frictionless

Entire System

• Unless otherwise stated, system starts at rest

Fundamental Rule For Strings

You can’t push on a string. Assume strings are always pulling

Pulley Solving Process

1. Find the direction of the acceleration. Who wins the tug of war?
2. Get $F_{net}$ equation of each mass.
3. Add the $F_{net}$ equations and isolate for $\overrightarrow{a}$