Goal 7 Work and Mechanical Advantage

What is Work? __WORK__ is when you exert a force on an object that causes the object to move some distance. Examples are Pushing a child in a swing, Picking a backpack up off the floor. No Work Without Motion To do __WORK__ on an object, the object __MUST__ move some distance as result of your force. If the object __DOES NOT MOVE__, __NO__ work is done, __NO MATTER__ how much force is exerted.

Force in the Same Direction To do __WORK__ on an object, the __FORCE__ you exert must be in the __SAME__ direction as the object’s motion. Carrying something: Since the force on the object is __VERTICAL__ () and the __MOTION__ is __HORIZONTAL__ ( ), you __DON’T__ do any work on the object as you carry it.

Calculating Work The amount of work done on an object can be determined by multiplying force times distance. Work = __FORCE__ X __DISTANCE__ Units of Measure: Force= __NEWTON’S__ ,Distance= __METER__ , Work = __JOULE’S__ BrainPop – Work (2:49)

POWER __POWER__ is the rate at which work is done. Power equals the amount of __WORK__ done on an object in a unit of __TIME__ More __POWER__ in same __TIME__ means __MORE WORK__ Calculating Power Power = __WORK__ / __TIME__ or __FORCE X DISTANCE__ / __TIME__ Power Unit Work is measured in __JOULES__ and time is measured in __SECONDS__, So a Joule per Second = __WATTS__ Brain Pop – Power (3:27)

How Machines DO Work A __MACHINE__ is a device that allows you to do work in a way that is easier. 3 ways a machine makes work __EASIER__: amount of __FORCE__ you exert, the __DISTANCE__ over which you exert your force, or the __DIRECTION__ in which you exert your force.

Input and Output Forces Input and Output Work The force you exert on the machine is called the __INPUT FORCE__ Input force __MOVES__ the machine The machine does work over a distance, called the __OUTPUT FORCE__ __INPUT FORCE__ X __INPUT DISTANCE__ = Input Work __OUTPUT FORCE__ X __OUTPUT DISTANCE__ = Output Work

Mechanical Advantage __MECHANICAL ADVANTAGE__ is the number of times a machine __INCREASES__ a force exerted on it. Mechanical Advantage = __OUTPUT FORCE__ / __INPUT FORCE__ Eureka! (4:51) http://www.youtube.com/watch?v=rvscbkd3AzU

Changing Force When a machine __INCREASES__ force, you must exert the __INPUT FORCE__ over a greater distance. When the __OUTPUT__ force is greater than the __INPUT__ force, the M.A. of a machine is __GREATER__ than 1

Changing Distance When a machine increases __DISTANCE__, you must apply a greater __INPUT FORCE__ For a machine that __INCREASE__ distance the __OUTPUT__ force is less than the input force.

Changing Direction When a machine changes the __DIRECTION__ of the input force, the amount of force and the distance __REMAINS THE SAME__ If only direction changes, the __INPUT__ force will be the same as the __OUTPUT__force. The M.A. will __ALWAYS__ be 1.

Efficiency of Machines The __EFFICIENCY__ of a machine compares the output work to the input work. Efficiency is expressed as a __PERCENT__ Calculating Efficiency Efficiency = __OUTPUT WORK__ / __INPUT WORK__ X __100%__ Real and Ideal Machines All machines have an __EFFICIENCY__ of __LESS__ than __100%__ 100% effieciency is called an __IDEAL MACHINE__