Physics: Torque, Simple Machines, and Mechanical Advantage

Torque does not equal work

Torque is rotational, work is linear

Why are doorknobs not in the middle?

Increasing distance from pivot increases torque

Greater distance from pivot

Requires less force to rotate

Angle that maximizes torque

90 degrees

Work equation

W = F × d

Work in an ideal machine

Work in equals work out

When friction is present

Work in is greater than work out

Purpose of simple machines

Change direction of force or multiply force

Simple machines never do

More work than input

Inclined plane purpose

Reduce force by increasing distance

Inclined plane example

Ramp

Inclined plane work

F in × d in = F out × d out

Lever

Fulcrum, effort, and load

Fulcrum

Support point of a lever

Lever force rule

Double distance gives half force

Torque

Ability to rotate an object around a fixed point

Pivot point

Fixed point an object rotates around

Lever arm

Perpendicular distance from pivot to force

Torque equation

T = F × lever arm

Torque depends on

Force, distance from pivot, and angle

Force that produces torque

Force perpendicular to lever arm

Parallel force effect

Produces zero torque

Lever example

Seesaw

Mechanical advantage

Force multiplication from a machine

Ideal mechanical advantage

Assumes no friction

Effect of friction

Reduces mechanical advantage

Wheel and axle

Simple machine using rotation

Wheel and axle example

Doorknob

Wheel and axle rule

Larger wheel reduces force needed

Screw

Twisted inclined plane

Screw example

Jar lid or bolt

Screw advantage

Increases distance to reduce force

Pulley

Simple machine using rope and wheel

Pulley purpose

Change direction or reduce force

Mechanical advantage of pulleys

Equals number of supporting ropes

Pulley example

Flagpole

Wedge

Two inclined planes back to back

Wedge purpose

Redirects force outward

Wedge example

Knife