24. Absorption of Gases by Liquids depends on molecular attraction and motion. Water at a temperature of 0° cen. (32° f.), is capable of condensing in its pores (17) six hundred times its own bulk of ammonia gas. The absorption of oxygen from the air causes some oils to become more viscous, to eventually become solid, without losing in weight, in fact sometimes gaining. Other oils dry up, or evaporate, leaving little or no residue.
25. Force.—Force is that which can produce, change or destroy motion.
We see a body move; we know there must be a cause; that cause we call force. We see a body in motion come to rest; this effect must have had a cause; that cause we attribute to force. The forces acting in machines are distinguished into driving and resisting forces. That component of the force which does the work is called the "effort."
26. Friction is usually a resisting (29) force, tending to destroy motion; but it is sometimes the means of the transmission of motion.
27. Work is the result of force acting through space. When force produces motion, the result is work. Work is measured by the product of the resistance into the space through which it is overcome.
28. Energy, which is defined[6] as the capacity for doing work, is either actual or potential. Actual or kinetic energy is the energy of an actually moving body, and is measured by the work which it is capable of performing while being brought to rest under the action of a retarding force.
Potential Energy is the capacity for doing work possessed by a body in virtue of its position, of its condition, or of its intrinsic properties. A bent bow or a coiled spring has potential energy, which becomes actual in the impulsion of the arrow or is expended in the work of the mechanism driven by the machine. A clock weight, condensed air and gunpowder are examples.
This form of energy appears in every moving part of every machine and its variations often seriously affect the working of machinery. (84.)
FOOTNOTES:
[5] This and some of the definitions that follow are adapted from "Elements of Physics" by A. P. Gage.