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Lec 11 | 8.01 Physics I: Classical Mechanics, Fall 1999

introduction
introduction work
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introduction work

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Description: The work-energy theorem is derived showing that the change in kinetic energy equals the work done on a particle by the sum of all forces. Gravity does negative work on an object thrown upwards until it reaches its maximum height of its trajectory.

explanation work in 3-dimensions
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explanation work in 3-dimensions

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Description: Work in 3D is shown to decompose into the sum of each 1D component.

explanation conservative forces
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explanation conservative forces

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Description: Work done by gravity while a particle moves upwards a vertical distance h is -mgh, regardless of the path taken. When the work done by a force is independent of the path, that force is called a conservative force.

explanation gravitational potential energy
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explanation gravitational potential energy

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Description: Potential energy and kinetic energy can be converted back and forth but their sum, the mechanical energy, is conserved if only conservative forces are involved.

problem
problem mechanical energy
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problem mechanical energy

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Description: The centripetal acceleration, when the roller coaster is upside down, must be greater than g; the mechanical energy must therefore exceed a threshold value.

explanation newtonian gravity
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explanation newtonian gravity

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Description: The gravitational force falls off as one over the distance squared. If large distances are involved, the gravitational potential due to an object of mass M is taken to be zero at infinity.

demonstration
demonstration conservation of mechanical energy
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demonstration conservation of mechanical energy

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Description: If released with zero speed, the wrecking ball should NOT swing higher than its height when it was released. Professor Lewin puts his life on the line by demonstrating this.

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References:

  1. 1D Work and Kinetic Energy - Walter Lewin, Lec 10 | 8.11 Physics I: Classical Mechanics, Fall 1999. (MIT Open Courseware), http://www.youtube.com/watch?v=CgqBg44azYk (Accessed 05/21/10). Ccbyncsa
  2. Work Calculated in 3-Dimensions - Walter Lewin, Lec 10 | 8.11 Physics I: Classical Mechanics, Fall 1999. (MIT Open Courseware), http://www.youtube.com/watch?v=CgqBg44azYk (Accessed 05/21/10). Ccbyncsa
  3. Gravity is a Conservative Force - Walter Lewin, Lec 10 | 8.11 Physics I: Classical Mechanics, Fall 1999. (MIT Open Courseware), http://www.youtube.com/watch?v=CgqBg44azYk (Accessed 05/21/10). Ccbyncsa
  4. When Gravity is the only Force - Walter Lewin, Lec 10 | 8.11 Physics I: Classical Mechanics, Fall 1999. (MIT Open Courseware), http://www.youtube.com/watch?v=CgqBg44azYk (Accessed 05/21/10). Ccbyncsa
  5. A Roller Coaster, Upside-down - Walter Lewin, Lec 10 | 8.11 Physics I: Classical Mechanics, Fall 1999. (MIT Open Courseware), http://www.youtube.com/watch?v=CgqBg44azYk (Accessed 05/21/10). Ccbyncsa
  6. Newton's Law of Universal Gravitation - Walter Lewin, Lec 10 | 8.11 Physics I: Classical Mechanics, Fall 1999. (MIT Open Courseware), http://www.youtube.com/watch?v=CgqBg44azYk (Accessed 05/21/10). Ccbyncsa
  7. Conservation of Mechanical Energy and a Wrecking Ball - Walter Lewin, Lec 10 | 8.11 Physics I: Classical Mechanics, Fall 1999. (MIT Open Courseware), http://www.youtube.com/watch?v=CgqBg44azYk (Accessed 05/21/10). Ccbyncsa