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One form of energy can be converted into another form of energy. Conservative and non-conservative forces CONSERVATION

Chapter 8: Potential Energy and Conservation of Energy part 2. Reading assignment: Chapter 9.1-9.4 Homework : (due Wednesday, Oct. 5, 2005): Problems: Q2, 3, 6, 15, 20, 22 . One form of energy can be converted into another form of energy. Conservative and non-conservative forces

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One form of energy can be converted into another form of energy. Conservative and non-conservative forces CONSERVATION

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  1. Chapter 8: Potential Energy and Conservation of Energy part 2 Reading assignment: Chapter 9.1-9.4 Homework : (due Wednesday, Oct. 5, 2005): Problems: Q2, 3, 6, 15, 20, 22 • One form of energy can be converted into another form of energy. • Conservative and non-conservative forces • CONSERVATION OF ENERGY

  2. Work due to friction If friction is involved in moving objects, work has to be done against the kinetic frictional force. This work is:

  3. Work done by non-conservative forces 1. Work done by an applied force. (System is not _____________) An applied force can _________ energy into or out of the system. Example. Applying a ____________ to an object and lifting increases the energy of the object.

  4. Black board example 7.4 • Angus is pulling a 10,000 kg truck with all his might (2000N) on a frictionless surface for 10.0 m. • How much work is the man doing? • What is the speed of the truck after 10 m. • What is the speed of the truck after 10 m if there is friction? • (friction coefficient: 0.0153)

  5. Power Power is the at which work is done: Average power: (work done per time interval Dt)

  6. The power can also be expressed as: (Dot product) The units of power are __________ (__/__) = watt (W)

  7. Black board example 7.7 • An elevator having a total mass of 3000 kg moves upward against the gravitational force at a constant speed of 9.13 m/s. • What is the power delivered by the motor?

  8. Review Important energy formulas: Work: Forms of energy:

  9. Black board example 8.2 • A mass m is bobbing up and down on a spring. • Describe the various forms of energy of this system. • At the highest point • At the point where the kinetic energy is highest • At the lowest point

  10. Black board example 8.3 Three balls are thrown from the top of a building, all with the same initial speed. The first is thrown horizontally, the second with some angle above the horizontal and the third with some angle below the horizontal. • Describe the motion of the balls. • Rank the speed of the balls as they hit the ground.

  11. Black board example 8.5 Nose crusher? A bowling ball of mass m is suspended from the ceiling by a cord of length L. The ball is released from rest when the cord makes an angle qA with the vertical. • Find the speed of the ball at the lowest point B. • Assume a cord length L = 5m and an angle qA = 20°. • The ball swings back. Will it crush the operator’s nose?

  12. Reading potential energy curves Remember:

  13. Black board example 8.6 • During a rock slide, a 520 kg rock slides from rest down a hillside that is 500 m long and 300 m high. The coefficient of friction between the rock and the hillside is 0.25. • What is the gravitational potential energy of the rock before the slide? • How much energy is transferred into thermal energy during the slide? • What is the kinetic energy of the rock as it reaches the bottom of the hill?

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