Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

OPERATION EXPLAINED.

As 4 the lesser diameter is to 48 the greater :: so is 2 the lesser power to the greater power to be raised by the axle.

Lesser. Greater. Lèsser.

4 48: 2 to a fourth number.

[blocks in formation]

If a wheel be 48 inches in diameter, the axle 4 inches, and 24 pounds are suspended from the axle, how many pounds must be applied to the rim of the wheel to balance the 24 pounds? Answer, 2 pounds. As 48 the greater diameter, is to 4 the lesser; so is 24 the greater power, to the lesser.

[blocks in formation]

If 120 pounds be suspended from an axle of 6 inches in diameter, and we have 10 pounds power to apply to the rim of the wheel, how many inches in diameter must the rim be that the 10 pounds will balance the 120?

Answer, 72 inches.

OPERATION EXPLAINED.

As 10 pounds the lesser power is to 120 the greater :: so is the lesser diameter: to the greater.

Lesser. Greater. Lesser.

10 : 120 :: 6 to a fourth number.

10)720(72 inches, diameter of the wheel.

SELF-MOVING MACHINE.

Sir ISAAC NEWTON observed, that "if ever the art of mak ing a perpetual motion should be discovered, it would be by some novice of inferior literary acquirements:" a very just observation undoubtedly; for, modern scholars have so much pomp and vain-glory to maintain, that they have but little time to spare for the good of rising generations: but let us attend to our subject.-Suppose a wheel to be of 20 feet diameter, with buckets some like the conductors of a flour-mill; and on the shaft by the side of this wheel let there be another small wheel, of about 4 or 5 feet in diameter, with cogs projecting outwardly; let there be two other small wheels, of a cylindrical form, rather smaller than the last mentioned, and place one of them directly above, and the other below the cogwheel, so that they all three shall stand in a direct line perpendicularly: let there be a strap with holes suitably formed to fay on those cogs, and let there be conductors on the strap to carry weights or balls, received from the bottom of the large wheel, to the top of the same, and into a conductor which will convey said balls to the buckets of the large wheel. To increase the velocity of the strap, add a small wheel to the cogwheel.

If Readhefar* had embraced this principle it would have saved him much credit, and would have at least improved bis skill in making running-gears for complicated machinery, if the project of perpetual motion had failed.

NOTE. This plausible theory originated by calculating the powers of the wheel and axle; but it is not delivered to the world as infallible or warrantable. However, if this project should fail, another may be tried with MAGNETISM, which still holds out an idea as plausible as the first. If Magnetism can be placed in such position or positions, as will destroy the counter attraction, or so that the attractive power will draw up on one side of the wheel, while the propelling power on the other side drives downward; then you may pronounce it an auxiliary which will bring about the desired effect.

* A man by the name of Readhefar, in the state of Pennsylvania, on or about the year 1813, undertook to exhibit a perpetual motion ; but with all

OF THE SCREW.

How to find the proportion in raising by a Screw, a weight greater than that of the power applied to the Lever.

[merged small][ocr errors]

When operating with a screw, we use a lever with the power applied to the end; and this end of the lever in going round describes a circle: multiply the length of the lever by 2, the product will be the length of the diameter of said circle. By Rule, page 331, multiply the diameter of a circle by 3.1416, or by 3.14159, the product will be the circumference.

RULES FOR THE SCREW.

1. As the circumference described by the end of the lever where the power is applied,

is to the distance the threads of the screw are apart; So is the weight to be raised,

to the power applied to the end of the lever.

LESSON 1.

If the threads of a screw be 2 inches apart, and we wish to raise 20 hundred weight with a lever 36 inches long, how great a power must be applied to the end of the lever? Answer, 19.8 pounds.

EXPLANATION.

36 inches the lever x 2 = 72 the diameter of a circle described by turning said lever.

3.1416 common multiplier,

72 diameter.

62832

219912

226.1952 circumference described by the lever. Threads of the screw 2 inches apart.

20 hundred x 112 = 2240 pounds to be raised.

his ingenuity in attempting to deceive the public, and gain a considerable sum of money to himself, he was detected by the celebrated ROBERT FULTON

[blocks in formation]

As the distance between the threads of the screw,

is to the circumference;

So is the power at the end of the lever,

to the weight raised.

LESSON 2.

Suppose the threads of a screw are or .5 of an inch apart, the length of the lever 15 inches, and a power of 10 pounds be applied to the end of the lever, how many pounds will be raised or supported in equilibrium by the screw, making no allowance for friction?

Answer, 1884.96 pounds.

[blocks in formation]

This is a power of resistance generated by the rubbing

of one thing against another.

The whole of the preceding calculations are independent of friction; for they are computed upon the same principle as though no such power existed. Yet in every of those operations with the lever, the wheel and axle, and the screw, less or more friction will be generated and become a power of resistance. It is rational to suppose that the least friction in these cases will arise from the lover; the next least from the wheel and axle, and a greater from the screw.

The proportion of friction is defined by philosophers thus, "It is in proportion to the weight and velocity,* conjointly, of the moving body." But suppose we should say, The friction of a moving body is in proportion to its weight, velocity, and formation, jointly considered.—We naturally suppose that different forms or shapes of a body, will cause different degrees of friction: It may be truc, that, a cubic polished body of metal will move on a level smooth surface with the same power applied as it would when formed into a parallelogram, or into a square plate of one third the thickness of the cubic form. But can we suppose that a lever on the edge of a fulcrum of suitable thickness, will create a resisting power by friction equal to the friction of a screw in raising the same weight, allowing the lever, the fulcrum, and screw, to be of one degree of hardness?

Experience and experiments must enable us to decide on such intricate and unascertained niceties.-The laws of friction are so various, that several pages of tables would be filled in elucidating its different powers in different operations and then an infinity of intervening cases might happen, where new rules would become necessary. For, by experiments it has been ascertained that friction in

Velocity, swiftness of motion.

This principle is asserted by writers on friction, but how they will dispose of attraction by cohesion, when two surfaces are put in contact, I cannot imagine, unless by oiling the parts before they are placed together. This may destroy attractive cohesion.

« ΠροηγούμενηΣυνέχεια »