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

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

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.

 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

 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?

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

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

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 )

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

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