Читать книгу A Treatise on Mechanics онлайн

63 страница из 91

Again, if B, fig.4., be a magnet moving in the direction BC with a certain quantity of motion, and while it is so moving a mass of iron be placed at rest at A, the attraction of the magnet will draw the iron after it towards C, and will thus communicate to the iron a certain quantity of motion in the direction of C. All the motion thus communicated to the iron A must be lost by the magnet B.

If the magnet and the iron were both placed quiescent at B and A, the attraction of the magnet would cause the iron to move from A towards B; but the magnet in this case not having any motion, cannot be literally said to transfer a motion to the iron. At the moment, however, when the iron begins to move from A towards B, the magnet will be observed to begin also to move from B towards A; and if the velocities of the two bodies be expressed by numbers, and respectively multiplied by the numbers expressing their masses, the quantities of motion thus obtained will be found to be exactly equal. We have already explained why a quantity of motion received in the direction BA, is equivalent to the same quantity lost in the direction AB. Hence it appears, that the magnet in receiving as much motion in the direction BA, as it gives in the direction AB, suffers an effect which is equivalent to losing as much motion directed towards C as it has communicated to the iron in the same direction.