# Unit 9: Work and Simple Machines

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Unit 9: Work and Simple Machines

The Meaning of Work In science you do work on an object when you exert a force on an object that causes the object to move some distance. Example: pushing a child on a swing

No Work Without Motion In order for you to do work on an object, the object must move some distance as a result of your force In other words: you can huff and puff, but if you don’t blow that house down, no work has been done.

Only Force in the Same Direction
In order to do work on an object, the force you exert must be in the same direction as the object’s motion. If the force is NOT in the SAME direction the object is moving, no work is done. NO WORK YES, WORK

Work or No Work? Test your understanding of work so far? 1) A snowstorm hits town and you go help your parent push your car out of the snow. You push as hard as you can but the car doesn’t budge 2) You carry a heavy bag of books to school everyday 3) You lift the bags of groceries from the cart into the trunk 4) You pull two kids on a sled 5) You pull the books out of a back pack 6) You hold a long piece of wood up at one end, while someone hammers the other end NO WORK NO WORK WORK WORK WORK NO WORK

Work is… 1)A force is exerted causing the object to move AND 2) The object is moving in the direction of the force

Calculating Work The amount of work you do depends on both the amount of force you exert and the distance the object moves: Work = Force (x) Distance W = F (X) D OR…. W F D

Work is Measured in Joules (J)
Force is measured in… Newtons (N) Distance is measured in… Meter (m) The SI (Systeme International) unit for work is the newton (x) meter = Joule (J) One Joule is the amount of work done to exert a force of 1 newton to move an object 1 meter

Why do we use machines…? To make work easier!!! A machine makes work easier by… changing the amount of force you exert, the distance over which you exert the force, or the direction in which you exert force In other words: a machine takes the effort required to move an object from point A to point B easier

Force and Machines When a machine does work the force exerted on the machine is called the… Input Force The machine exerts a force over some distance, the force exerted by the machine is called… Output Force

Mechanical Advantage When input force is compared to output force you are determining the advantage of using a machine. A machine’s mechanical advantage is the number of times a force exerted on a machine is multiplied by the machine Consider it this way…

Mechanical Advantage (MA) = Output Force ÷ Input Force
Scenario 1: Can Opener You exert 20 newtons of force on an can opener which in turn exerts 60 newtons on the can. ÷ = 3 Output Input MA The can opener triples the work done! Scenario 2: Piano It would take 3,200N to lift a piano up on to a stage. Instead you use a ramp which requires 1,600N. 3,200 ÷ 1,600 = 2 Output Input MA The ramp doubles the force you exert.

Efficiency of Machines
Ideally, we would want to put in a minimal amount of input force and get out multiple amounts of output force. However, we know this isn’t true. Some work is wasted overcoming friction, tightness of parts, or the “design” of machines -Poor design!

Simple Machines Paul Wants Work In Life to be Simple
Remember this sentence There are six basic kinds of simple machines: Paul Wants Work In Life to be Simple Pulley Wedge Wheel & Axel Inclined plane Lever Screw

1) Pulley Grooved wheel in which a rope, chain, or cable is pulled to raise an object. Examples: Window blinds, flagpole

2) Wedge A triangular devise used to split or push objects apart A wedge can be considered two inclined planes Examples: Axe, zipper

3) Wheel & Axel Two circles that are attached to one another and that rotate about a common axis. Used for transporting of objects. Examples: Cars, Door handles

4) Inclined Plane A flat, slanted surface used to lower or raise objects. The longer the ramp, the more mechanical advantage. Example: hallway ramp

5) Lever A rigid bar that is free to pivot, or rotate about a fixed point. A lever works in two ways: 1) it increases the effect of input force and, 2) it changes direction of the input force Examples: Spoon, door handle, crow bar

6) Screw An inclined plane wrapped around a cylinder. Used to connect to objects The closer the thread on any screw the greater the mechanical advantage Examples: Faucets, jar lids

Rube Goldberg Machines
A Rube Goldberg machine, contraption, invention, device, or apparatus is a deliberately over-engineered or overdone machine that performs a very simple task in a very complex fashion, usually including a chain reaction. The expression is named after American cartoonist and inventor Rube Goldberg (1883–1970). -Wikipedia Examples: Bowling Example(good) Better Rube meets simple machine And the greatest mix of science and music(best!)

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