Friction, Lubrication and the Lubricants in Horology

by W. T. Lewis

ELEMENTARY PHYSICS RELATING TO FRICTION AND LUBRICATION.

15. Most of those who may read this work, are no doubt familiar with the laws of elementary physics; but as all may not be, for a better understanding of that which follows, it may be well to treat briefly of some of the physical laws bearing on the subject.

16. The Molecule.[5] Every visible body of matter is composed of exceedingly small particles called molecules. This is the basis of the theory of the constitution of matter which physicists have usually adopted. It is estimated that if we should attempt to count the number of molecules in a pin's head, counting at the rate of 10,000,000 per second, we should require 250,000 years.

17. Porosity. The term pore in physics is restricted to the invisible space that separates molecules. All matter is porous; thus dense gold will absorb (24) liquid mercury, much as chalk will water; but the cavities to be seen in a sponge are not pores.

18. Gravitation. That attraction which is exerted on all matter, at all distances, is called gravitation. Gravitation is universal, that is, every molecule of matter attracts every other molecule of matter in the universe. The whole force with which two bodies attract one another is the sum of the attraction of their molecules, and depends upon the number of molecules the two bodies collectively contain, and the mass of each molecule. Hence, all bodies attract, and are attracted by, all other bodies.

In a ball suspended from the ceiling by a thread an attraction exists between the ball and the ceiling, but on account of a greater attraction existing between the ball and the earth, if we cut the thread the ball will move toward the earth, or in the direction of the greater attraction.

19. The Effect of Distance. Gravitation varies inversely with the distance by which two bodies are separated.

As the sun is many times greater than the earth, the attraction between the ball (18) and the sun would cause the ball to leave the earth and move toward the sun were it not for the fact that the ball is so much nearer to the earth than to the sun.

20. Cohesion. The attraction which holds the molecules of the same substance together so as to form larger bodies is called cohesion.

It acts only at insensible distances and is strictly a molecular force. It is that force which prevents solid bodies from falling apart. Liquids like molasses and honey possess more cohesive force among the molecules of which they are composed than limpid liquids like water and alcohol. The former are said to be viscous, or to possess viscosity.

21. Adhesion. That force which causes unlike substances to cling together is called adhesion. It is that force which keeps nails, driven into wood, in their places. You can climb a pole because of the adhesion between your hands and the pole. We could not pick anything up if it were not for adhesion. Glue, when dry, possesses both cohesion and adhesion to a great degree.

22. Capillarity. Examine the surface of water in a vessel. You find the surface level, except around the edge next the glass, as at A (Fig. 7.)

Fig. 7.

Fig. 8.

1. Thrust vertically into water three glass tubes, A, B and C (Fig. 8), open at both ends. You notice the water ascends in each to a different height, and that the ascension varies inversely as the diameter of the bore; i. e., the smaller the bore, the higher the water ascends.

2. Seal one of the tubes at its upper end. The water enters but little, as shown at D (Fig. 8), on account of the resistance of the air pressure within the tube.

3. Thrust vertically two plates of glass into water, and gradually bring the surfaces near to each other. Soon the water rises between the plates, and rises higher as the plates are brought nearer. If their surfaces be mutually parallel and vertical, the water rises to the same height at all points between the plates, as shown at A (Fig. 9.)

Fig. 9.

4. If the plates be united by a hinge, and form an angle, the height to which the water ascends increases as the distance between the plates decreases up to their line of junction, where it attains a maximum, as shown at B (Fig. 9.)

5. Decrease the angle between the plates, and the water ascends higher, as shown at C (Fig. 9.) Thus it is seen that the ascension varies inversely with the angle between the plates; i. e., the smaller the angle, the higher the water ascends.

6. When a drop of oil is placed between two glass plates arranged as shown at A (Fig. 10), if the surfaces are not too far distant, and if the oil touches both surfaces, it will be seen to work its way to the junction of the plates; showing that oil between surfaces has a tendency to flow towards the apex of the angle.

Fig. 10.

7. Place a drop of oil on a taper piece of metal, as shown at B (Fig. 10). The oil will gradually recede from the point to a place where there is more metal, showing that oil on surfaces has a tendency to flow towards the largest part.

Fig. 11.

8. When a drop of oil is placed between two watch glasses arranged with flat and convex sides adjacent, as at A (Fig. 11), or with convex sides adjacent, as at B (Fig. 11), if the glasses are rigidly fixed in their relative positions the drop of oil can be shaken from its location only with great difficulty; the oil at C holding its place with greater tenacity than the oil at D.

The foregoing phenomena are called capillary action, or capillarity. Capillary action is due to the forces of cohesion (20), and to the forces of adhesion (21.)

23. Centrifugal Force.—The tendency of a body rotating round a point to escape from that point is called centrifugal force.

Place a small quantity of oil on the arm of a balance, near the arbor. Rotate the wheel rapidly. The oil is seen to flow towards the rim of the wheel.

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.)