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Chapter 9: Q6 CQ (page 314)

A round pencil lying on its side as inFigure 9.13is in neutral equilibrium relative to displacements perpendicular to its length. What is its stability relative to displacements parallel to its length?

Short Answer

Expert verified

On the flat surface the displacement is parallel to the pencil’s length, so it is neutral equilibrium.

On the tilted surface, the pencil moves to unstable equilibrium.

Step by step solution

01

Equilibrium

Equilibrium is described as a condition of rest in which nothing changes. There will be no positive or negative energy transfers in a balanced body.

02

Explanation on the flat surface case

When the pencil is resting on a flat surface, and the final and the initial position of the pencil is shown in the figure below:

Hence, the pencil’s potential energy remains the same as before, continuing neutral equilibrium.

03

Explanation on the tilted surface case

In the case of a tilted surface, the pencil slides down the slope of the floor, and it gets an acceleration.

Hence, the pencil is in unstable equilibrium with potential energy changes and the displacement parallel to its length.

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