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PHYSICS 103: Lecture 12

PHYSICS 103: Lecture 12. Agenda for Today:. Review of Example Problems Energy and Work. Work. Work is done whenever a force causes motion or a change in motion. Work = force . distance ( both in same direction ). Units = N m = Joules. Energy. Stored Work. Work waiting to happen.

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PHYSICS 103: Lecture 12

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  1. PHYSICS 103: Lecture 12 Agenda for Today: • Review of Example Problems • Energy and Work

  2. Work • Work is done whenever a force causes motion or a change in motion • Work = force . distance (both in same direction) Units = N m = Joules

  3. Energy • Stored Work • Work waiting to happen • The ability to do work • Also measured in Joules

  4. Energy comes in different Forms Some common examples: • Kinetic Energy(KE) • Gravitational Potential Energy • Internal Energy - friction, air resistance • Elastic Potential Energy - springs • Also measured in Joules

  5. Kinetic Energy • Energy of Motion

  6. Gravitational Potential Energy • Energy due to height when gravity is present

  7. Energy Conservation Energy cannot be created or destroyed; it may be transformed from one form to another but the total amount of energy never changes.

  8. Consider a single pendulum with a ball attached to a string E = PE = mgh E = PE = mgh m v h h E = KE = 1/2mv2

  9. Test your understanding: The pendulum bob has a mass of 0.5 kg and is released from a height of 12 cm relative to the low point in the swing. What is the speed of the bob as it passes through the low point? m = 0.5 kg h = 12 cm v = ? Initial Energy is PE = mgh = 0.5 kg  9.8 m/s2  0.12 m = 0.588 J Energy at low point is KE = 0.588 J 1/2mv2 = 0.588 J

  10. Roller Coasters History of the roller coaster - Russian Ice Slides ~ 80 feet

  11. Some current coasters

  12. Roller Coaster Design: Some Simple Physics Energy is conserved => Energy at top = Energy at bottom

  13. (KE + PE)top = (KE +PE)bottom • (1/2)mv12 + mgh = (1/2)mv22 + 0(1/2)v12 + gh = (1/2)v22 • (1/2)(8.8)2 + 9.8(95) = (1/2)v22 • 38.72 + 931 = (1/2)v22969.72 = (1/2)v221939.44 = v22v2 = 44.04m/s ...at the bottom the the 1st hill. (assuming no friction)

  14. Main Points from Today’s Lecture • Energy, Work and Energy Conservation • You should understand that work is defined as the product of the component of the force along the line of motion and the distance the object moves as a result of the force. You should understand that energy is “stored work”. It comes in different forms and it can never be created or destroyed. It just changes forms. You should be able to solve problems involving these concepts.

  15. Read Ch. 6 HW CH6: Q1,Q2,Q4,Q5,Q6,Q7 E1,E2,E3,E4, E5, E7,E10,E11,E13,E15,CP1

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