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Let us imagine a rod resting on a

__frictionless horizontal surface__such that the rod is made up of

__2 identical molecules__. Let these molecules be named A and B from left to right. If we pull A to the left and B to the right with

__forces of equal magnitude__, the rod must remain at

__equilibrium__according to

*Newton's First Law of Motion*. This means that A and B must remain at equilibrium as well. Then, when A and B are pulled in opposite directions, an

**attractive intermolecular force**will be exerted between A and B to cancel out the externally applied forces. This is consistent with the

*Lennard-Jones model*since the intermolecular force was

__attractive__when the distance between the molecules

__exceeded__the

**equilibrium distance**. The rod remains at equilibrium, but it becomes

__larger in length__after the

**outward**forces are applied.

A similar result would be obtained if the forces were directed

**inwards**instead. In this case, the intermolecular force would be

__repulsive__to cancel out the externally applied forces. Also, it would be consistent with the

*Lennard-Jones*model since the distance between the molecules became

__less__than the

**equilibrium distance**. The rod remains at equilibrium, but it becomes

__shorter in length__after the inward forces are applied.

Is this true?

Weam Abou Hamdan

Thursday, August 2, 2018