Work and Simple Machines Chapter 19 Section 3

Work When a force causes an object to move in the same direction of the force that is being applied Does effort always equal work? Calculating Work Work = force x distance or W = F*d Units as Force is measured in newtons (N) and distance in meters (m), thus work is measured in joules (J)

Calculating Work A weight lifter lifts 500-N weight at distance of 2 m from the floor to a position over his head. How much work does he do? Where w = F*d

Calculating Work Using a force of 50 N, you push a computer cart 10 m across a classroom floor. How much work did you do? Work

Machine What is a machine Simple machine Compound Machine A device that helps you do work Simple machine A machine that uses only one movement Ex: Screwdriver, inclined plane, wedge, wheel, axel Compound Machine A combination of simple machines Ex: can opener How do machines make things easier Increase the amount of force Can change the direction of the force

Mechanical Advantage Work In and Work Out The number of times the applied force is increased by a machine Mechanical advantage = output force/input force Or MA = Fo/Fi Work In and Work Out In simple machines the input and output force do work Ex: Can opener the output force is at the blade puncturing the can Ideal world there is no friction and work in = work out

Combination of Pulleys The Pulley Pulley – an object with a groove, like a wheel, with a rope or chain running through the groove Changes the direction of the input force Pulley Combination of Pulleys Simple pulley 50 N 100 N 50 N 50 N 100 N 100 N 100 N

Lever – a rod or plank that pivots about a fixed point Can increase force or increase the distance over which the force is being applied 3 classes of lever 1st class: Fulcrum – located between the input and output force (usually used to increase force) 2nd class: the output force is between the input force and the fulcrum (output force always greater than the input) 3rd class: the input force is between the output force and the fulcrum (MA < 1, increase the distance over which the input force is applied) Lever, Wheel and Axel

The Inclined Plane Inclined Plane – sloped surface, sometimes called a ramp. Allows for heavy lifting by using less force over a greater distance Work remains the same whether a ramp is used or a straight lift The longer the ramp the less force is needed to move the object Where in ancient history could ramps have been useful? Inclined plane

Wedge – moving inclined plane with one or two sloping sides Changes the direction of the input force Ex: knife, axe Screw – an inclined plane wrapped around a post. Changes the direction of the force you apply Ex: winding road around a mountain