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EPE – Calories- Law of Conservation of Energy and Work-Energy Theorem

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Another type of PE is… Elastic Potential Energy( EPE) Energy stored in an obj. at its stretched or compressed state. Obj. will return to its original or relaxed length.

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EPE or Uel = ½ k x 2 EPE - elastic potential energy, J k - spring constant- STIFFNESS, N/m (indicates how easily a material stretches or compresses ‘higher k stiffer material’ x – the distance the spring is stretched or compressed from relaxed length ( x = ℓs - ℓr ) or ( x = ℓr - ℓc ) ( ℓr = relaxed length ) ( ℓs = stretched length ) or ( ℓc = compressed length ) Elastic Potential Energy

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Work can’t be done w/out _____________. The unit for Energy is ______________. The UNIT of HEAT ENERGY is calorie. It is = to 4.18 J ( Note the small “c” ) A calorie is the heat necessary to raise the temperature of 1 g of water 1°C. The UNIT for FOOD ENERGY is Calorie. (Note the Big “C” ) 1 Calorie = 1000 calories So, Where do Calories fit in w/Energy?

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Energy cannot be created nor destroyed, only changed to another __________. Same as the Law of Conservation of Mass Mass/ Matter in a closed syst. cannot be created nor destroyed only conserved. Law of Conservation of Energy

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Law of Conservation of Energy states.. The total energy of a closed, isolated system is constant KE 1 + GPE 1 + EPE 1 = KE 2 + GPE 2 +EPE 2 OR + mgh 1 + ½ kx 1 2 = + mgh 2 + ½ kx 2 2 ½ mv 1 2 + mgh 1 + ½ kx 1 2 = ½ mv 2 2 + mgh 2 + ½ kx 2 2 OR GPE(t)op + KE(t)op = GPE(b)ottom + KE(b)ottom

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Work-Energy Theorem-KE According to the Work-Energy theorem, the work done on an object, by the net force acting on it, is equal to the change in kinetic energy of the body Work = Δ KE F*d = KE f – KE i F*d = ½ m v f 2 – ½ m v i 2 F*d = ½ m (v f 2 – v i 2 )

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Work Energy Theorem-GPE When work is done, potential energy can also be changed.

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The unit to measure work is ___________ The two requirements: 1. 2. Example: How much work is done if the guy pushes with 40 N to move the 20 N box.

The unit to measure work is ___________ The two requirements: 1. 2. Example: How much work is done if the guy pushes with 40 N to move the 20 N box.

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