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Review For Exam #1

# Review For Exam #1 - Einsteins Big Idea Nova program about...

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Einstein’s Big Idea Nova program about the story of E=mc 2 But they go back to the origins of our modern understanding about energy including discussions of scientists like Michael Faraday, Antoine Lavoisier and Emilie du Chatelet Emilie in particular had the insight that the kinetic energy of an object was proportional to the square of its speed KE = 1 2 mv 2

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Power We defined power as So it must have units of energy over units of time (J/s) We name the units of power (J/s) after James Watt, the developer of the steam engine Often will talk about kilowatts or megawatts Note that your electric bill tells you not how many watts you used, but how many kilowatt- hours power X time = unit of energy Power = work done time interval another illustrious Scotsman 1 kw-hr=1000 J/s * 3600 s = 3.6X10 6 J
Simple machines A machine is a device for multiplying forces or simply changing the direction of forces The principle underlying every machine is the conservation of energy One simple machine is the lever A force downwards on one side creates and upward force on the other side But that’s not the big deal The big deal is that work input = work output (ForceXdistance) input = (ForceXdistance) output It’s a way of multiplying force, although the movement on the input side has to be larger Fxd ( ) input = ( Fxd ) output With the car jack, a 50N force acting over 25 cm becomes a 5000N force acting over 0.25 cm fulcrum

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Archimedes Discovered the principle of the lever and once stated “Give me a lever and I can move the world” Also discovered the principle of bouyancy and is credited with shouting “Eureka*” as he ran naked from his bath, after discovering this principle *“I have found it”
Pulleys A simple pulley can be used to change the direction of a force With this arrangement, a load can be lifted with half of the input force (the tension in the rope provides the other half) A block and tackle is a system of pulleys that multiplies force Note that energy is not multiplied. It takes the same amount of work to raise the 500 N weight

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Efficiency Mostly we’ve been talking about ideal machines, where 100% of input energy goes to output work But in any real transformation of energy, some energy is
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Review For Exam #1 - Einsteins Big Idea Nova program about...

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