All bodies on the earth, by virtue of the attraction of gravitation, tend to the centre of the earth. A ball held in the hand presses downward; if dropped, it descends perpendicularly; if placed on an inclined plane, it rolls down, in doing which it presses the plane with a part of its weight. In the air bodies fall with unequal velocities, a piece of paper, for instance, more slowly than a ball of lead; and it was formerly thought that the velocity of the fall of bodies was in proportion to their weight.
This error was attacked by Galileo, who, experimenting with balls of different substances which he dropped from the tower of Pisa, was led to the conclusion that the resistance of the air acting on different extents of surface was the cause of the unequal velocities, and that in a vacuum all bodies would fall with the same velocity. The truth of this last proposition wag first demonstrated by Isaac Newton in his celebrated 'guinea-and-feather' experiment, where a guinea and feather are shown to fall side by side in the vacuum of the air-pump. This experiment proves that the force of gravitation in bodies is proportional to their inertia, that is to their mass. The laws of falling bodies, that is of bodies falling freely in a straight line and through a distance short in comparison with the earth's centre, are the following:
1. When a body falls from rest it acquires velocity at the rate of about 32.2 feet per second. This number, which represents the acceleration due to the force of gravity, varies slightly with the locality, increasing from the equator to the poles, and diminishing as we recede from the centre of the earth. At the end of five seconds, therefore, the body would be found to be moving at the rate of 5 x 32.2, that is 161 feet per second.
2. The space fallen through in the first second is half of 32.2, that is 16.1 feet; and the space fallen through in any given time is found by multiplying the square of the number of seconds by 16.1. Thus, in three seconds a body falls 9 x 16.1 feet, or 144.9 feet.
3. The square of the velocity acquired by falling through any number of feet is found by multiplying twice that number by 32.2. Thus if a body falls 9 feet, the square of the velocity acquired is 2 x 32 x 9, or 576 feet per second, 32 being used instead of 32.2; and taking the square root of 576, we find that a velocity of 24 feet is acquired in a fall of 9 feet.
4. When a body is projected vertically upward with a given velocity, it continues to rise during a number of seconds found by dividing the number that expresses the velocity of projection by 32.2; and it rises to a height found by dividing the square of that number by 2 x 32.2, or 64.4. Research Fall of Bodies
The Eiffel tower is a structure named after its builder and is one of the most iconic sights of Paris. At the time of its construction it was by far the loftiest structure in existence, surpassing the WashingtonObelisk, the next highest by 430 feet. It cost about 260,000 pounds to build, and was erected partly at the cost of the state, partly by funds provided by Eiffel himself, who formed a company for the purpose - the company drawing funds through the fees which visitors had to pay. The top may be reached by stairs and lifts. The first stage or platform is at the height of 189 feet, and forms a quadrilateral 213 feet square, fitted up as a restaurant. The next platform is at the height of about 380 feet, and is 98 feet square. The third platform is at the height of 906 feet, and is large enough to accommodate a good number of persons, affording a magnificent view. The lantern higher up is supplied with powerful electric search-lights, and on the very summit is a small area utilized chiefly for scientific observations. The tower has been utilized for various scientific purposes (the fall of bodies, vibration of the pendulum, pressure of the air, etc). Research Eiffel Tower
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Fall of Bodies
