Work Work is done when a force moves an object

over a distance Work = force X distance or W = f X d

When a force is applied to an object, the force may or may not cause the object to move. If the force does not produce motion, NO WORK IS DONE! A force results in work ONLY if motion is produced.

Machines A device that transfers mechanical energy

from one object to another Make work easier to perform by:

1) multiplying force 2) changing the direction or the distance over

which a force is applied Ex: a wrench multiplies applied force when moving

a tight bolt. Ex: a loading ramp attached to the back of the

truck reduces the force but increases the distance the object must be moved.

Resistance and EffortResistance = the force a machine has

to overcomeEffort = the force appliedUsing a machine CAN reduce the

amount of effort needed to overcome a given amount of resistance but a machine does NOT decrease the amount of work

WorkEx: Suppose you lift a box weighing 450

Newtons up onto a 2 meter high platform. To light the box straight up by yourself, you would need to apply 450 Newtons of force over a distance of 2 meters. W= f x d = 450 N x 2 m = 900 J

Work HOWEVER, if you set up a rope and pulley

system to change the direction and distance of the force required, you might have to pull in 9 meters of rope only using 100 Newtons of force: W= f x d = 100 N x 9m = 900 J

So the TOTAL amount of work is the SAME using the pulley versus not using the pulley

6 Simple MachinesLeverPulleyWheel and axle Inclined planeWedgeScrew

LeverConsists of a rigid bar that can turn

around a point called a fulcrum Ex: pliers, crowbar

PulleyA modified form of a lever. Can change

direction of force or decrease the force needed to move a heavy object. Ex: clothes line

Wheel and axleA modified form of a lever. Consists of

a large wheel with a smaller wheel (or axle) in its center. They are connected so they turn together. Turning the outer wheel uses less force but must turn a greater distance. Ex: bicycles, car steering wheels,

doorknobs

Inclined planeA flat surface with one end higher than

the other. Ex: wheelchair ramp, truck ramp

WedgeDouble-sided inclined plane. The effort

force is applied by driving the wedge into something, like an ax into a log. Ex: ax, knives, wood nails, chisels

ScrewAn inclined plane wrapped around a

wedge or cylinder Ex: wood screws, bolts, car jacks

Complex MachinesContains 2 or more simple machines

Ex: a bike has a wheel and axle, a pulley system and a lever.

Efficiency of machinesMachines are never 100% efficientThe amount of work done by any

machines is ALWAYS less than the amount of work put into it

Some work is converted into heat energy and is wasted. Heat energy is produced because of rubbing together of the machine’s parts (friction).

Machine efficiencyA machine can be made more efficient

by reducing friction.Grease oil, and wax are good ways to

reduce the friction between moving parts.

Sanding surfaces to make them smoother or using ball bearings between surfaces also reduces friction.