First Principles of Mechanics.

The science of mechanics, in its most extensive sense embraces a large proportion of what is termed Natural Philosophy, or the system of laws which govern the various operations of Nature. It investigates the laws and effects of Inertia, force, motion, momentum, gravity, & c.

Inertia is that which constitutes in all bodies or substances, a tendency when at rest, to remain at rest; and when in motion to continue in motion independent of any force or power. But as every moving body is opposed to have been put in motion by some moving power, its inertia in this case becomes momentum.

Illustration-if a round ball is placed on a table that is perfectly level, it will remain at rest, and will require the application of power or force to put it in motion; but when this ball is put in motion, it will require some resistance to stop its motion.

Gravity is that property which consists in all bodies a tendency to move towards each other, and especially, towards the centre of the earth; it is always in direct proportion to inertia. Gravity is generally considered to be merely the attraction of the earth; it consists of the force by which bodies descend towards the earth when suspended, or are let go from a height; and this force constitutes weight.

Illustration-If a ball be suspended by a cord, it will uniformly hold the cord in a position at right angles with the surface of the earth. If the point from which the ball is suspended be fixed, and the ball be removed any distance from its natural position, it will, when liberated, return to its natural position directly under the point of suspension; but in this instance, it will not readily stop at the point of its natural position; but having received an impulse from the force of gravity, its momentum will force it some distance beyond the given point, until this momentum is again overcome by gravity; then gravity again impels it in a contrary direction, and it is again carried beyond by its inertia. Thus a vibratory motion is for some time continued, before the ball becomes stationary. Here are illustrated by one example, Gravity, Inertia, Motion and Momentum.