## Lecture 25: Static Equilibrium - Stability - Rope Walker

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: November 1999,   views: 21210
released under terms of: Creative Commons Attribution Non-Commercial Share Alike (CC-BY-NC-SA)

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# Description

1. Rotation vs. Translation:

The analogy between rotational and translational equations is summarized.

A ladder leaning against the wall is analyzed to determine the minimum angle it can make with the floor without sliding. The ladder is then set at this critical angle, and the stability is investigated as someone climbs the ladder.

3. Rope Tension Reduced by Friction:

Sailors often wind a rope around a cylinder to reduce the tension that needs to be applied to hold an object in place. The tension is reduced by friction along the wrapped portion of the rope. You can use this device to balance a strong force. Professor Lewin has constructed a device that demonstrates this in a very dramatic way.

4. Locating the Center of Mass of a Rigid Body:

The center of mass always lines up below the point of suspension such that the net torque (relative to the suspension point) is zero. When the center of mass is positioned below the point of suspension, the system is stable.

5. Stability of a Rope Walker:

The stability of a rope walker is improved by lowering her center of mass below the rope. If the walker also wears special shoes so that she can't slide sideways off the rope, she cannot fall.

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