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Nonconservative Forces

Nonconservative Forces. Conservation Law. In the work-energy principle, the work is divided into conservative and non-conservative forces. Kinetic energy D K = W con + W non The conservative forces have a related potential energy. Kinetic energy D K = - D U + W non.

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Nonconservative Forces

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  1. Nonconservative Forces

  2. Conservation Law • In the work-energy principle, the work is divided into conservative and non-conservative forces. • Kinetic energy DK = Wcon + Wnon • The conservative forces have a related potential energy. • Kinetic energy DK = -DU+ Wnon DK + DU = Wnon

  3. The conservation of energy includes nonconservative forces. These are also called dissipative forces. The work done is always negative. The work dissipates energy. Other Forms of Energy d F = -mFN -d F = mFN

  4. Conservation of Energy • Nonconservative forces do not violate the conservation of energy. • The energy has taken another form. • Molecules vibrate more • This becomes internal energy or heat

  5. The hill is 2.5 km long with a drop of 800 m. The skier is 75 kg. The speed at the finish is 120 km/h. How much energy was dissipated by friction? Using Friction and Energy q

  6. Find the total change in kinetic energy. Find the total change in potential energy. The difference is due to friction and drag. DK = ½ mv2 - 0 = ½(75 kg)(130 m/s)2 = 5.4 x 105 J DU = mgh = (75 kg)(9.8 m/s2)(-800 m) = -5.9 x 105 J Wnon = DK + DU = -0.5 x 105 J Friction and Height

  7. Friction and Springs • The dissipation of energy due to friction also affects the mechanical energy in a spring. • If the car stopped, the bumper dissipated the energy. v 980 kJ initial kinetic energy x 980 kJ dissipated energy next

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