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# Work And Energy

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### Work And Energy

1. 1. Work and Energy<br />It takes energy to do work.<br />
2. 2. Work – Force X Distance<br />Energy is what makes things move. <br />When you move something you do work. <br />The amount of energy it takes to move something depends on the force exerted and the distance it is moved.<br />Work (change in energy)= force X distance <br />Impulse (change in momentum) = force X time.<br />Ex: Lift a barbell over your head = work is done on barbell<br /> Hold the barbell over your head ≠ work is not done on barbell<br />Units for work: Newtons x meters (N∙m) <br />1 N∙mis equal to 1 joule – the energy to pick up a ¼ pound cheeseburger from the table to above your head.<br />
3. 3. Power – How Quickly Work Gets Done<br />Power is the rate at which work is done.<br />Power = work done<br /> time<br />The unit of power is the joule per second (j/s), or the watt (W).<br />Ex: One watt of power is used if you lift that cheeseburger in one second.<br />1kilowatt (kW) is 1000 watts, 1 megawatt (MW) is 1,000,000 watts.<br />
4. 4. Mechanical Energy <br />Mechanical energy is the ability to do work on an object (make it move)<br />The unit it ismeasured in is joules (j).<br />Mechanical energy (work) can be in the form of potential and/or kinetic energy.<br />
5. 5. Potential Energy – Stored Energy<br />Potential Energy (PE) is energy that is stored in ready position and has the potential to do work.<br />Work = force x distance<br />Gravitational PE = weight x height. <br />PE = mass x gravity x height (mgh)<br />Ex. A rock at the top of a hill, a bow pulled back, a compressed spring.<br />
6. 6. Kinetic Energy – Energy of Motion<br />Kinetic Energy (KE) depends on an object’s mass and speed.<br />KE = ½ mass x speed2 (½mv2)<br />Ex. A moving car has kinetic energy, a car moving twice as fat twice the speed has 2v2or four times the KE.<br />To change the kinetic energy of an object work must be done on it. The change in kinetic energy (∆KE) = Work<br />
7. 7. Conservation of Energy <br />Energy comes in many forms: heat, light, sound, electricity, and radioactivity.<br />The law of conservation of energy:<br />Energy cannot be created or destroyed; it may be transformed from one form into another, or transferred from one object to another, but the total amount of energy never changes.<br />Ex. Eat a cheeseburger (chemical energy) -> body heat.<br />