## Lecture 18: Exam Review 2

author: Walter H. G. Lewin, Center for Future Civic Media, Massachusetts Institute of Technology, MIT
recorded by: Massachusetts Institute of Technology, MIT
published: Oct. 10, 2008,   recorded: October 1999,   views: 17190
released under terms of: Creative Commons Attribution Non-Commercial Share Alike (CC-BY-NC-SA)

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# Description

1. Work-Energy Theorem:

The conservation of mechanical energy applies when there are only conservative forces. The work-energy theorem always applies (also when non-conservative forces, such as friction, operate). A block on an inclined plane with friction is analyzed to solve for the coefficient of static friction. The work-energy theorem is shown to provide an elegant solution to solving for the block's velocity.

2. Bizarre Spinning Top - Part I:

A top is spun on the desk in the lecture hall to show that friction dissipates the top's kinetic energy into heat (the friction does negative work), and the top quickly falls over. Professor Lewin then spins the same top on a small magic black box. The top does not fall over, how bizarre!

3. Pendulum, Work and Energy:

A pendulum problem is discussed with a set of initial conditions. The maximum angular swing of the pendulum is calculated using the initial conditions and the conservation of mechanical energy. The work-energy theorem gives the same result. Numerical results are obtained for both the maximum angular swing and the phase angle.

4. Bizarre Spinning Top - Part II:

Fifteen minutes later the top is still spinning. How on Earth is this possible?

5. Spring, SHO and Initial Conditions:

Conservation of mechanical energy is used to calculate the maximum displacement of an object attached to a spring for given initial conditions.

6. Newton's Law of Universal Gravitation:

The orbital speed of the Earth around the sun is calculated. The kinetic and potential energies of the Earth are reviewed. The escape velocity, to leave the solar system is discussed.

7. Resistive Forces, Viscous Term:

This segment reviews concepts and measurements from lecture 12 such as the viscous and pressure drag terms, the terminal velocity, and the critical velocity.

8. Collisions and Conservation of Momentum:

In the absence of a net external force on a system, momentum of the system as a whole is conserved even when objects in the system collide and when kinetic energy is destroyed (a rather non-intuitive concept).

9. Bizarre Spinning Top - Part III:

The top has been spinning now for over 30 minutes; what's going on?

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