Page 256 - Third Book of Reading Lessons

READING LESSONS. 255 E A.-That cannot be much, I think.
FATBER.-Perhaps, with regard to the ball struck om your brother's trap, it is of no great considera­ tion, because the velocity is but small; but in all great velocities, as that of a ball om a musket or cannon, there will be a material di erence between the theory and practice, if it be neglected in the cal­ culation. :Move your mamma's riding-whip through the air slowly, and you observe nothing to remind you that there is this resisting medium; but if you swing it with considerable swiftness, the noise which it occasions, will in rm you of the resistance it meets with om something, which is the atmosphere.
CnARLEs.-If I now understand you, the rce which compels a body in motion to stop, is of three kinds: (1) the attraction of gravitation;-(2) the re­ sistance of the air;-and (3) the resistance it meets with om iction.
FATBER.-Yon are quite right.
CnARLEs.-I have no di culty of conceiving, that a body in motion will not come to a state of rest, till it is brought to it by an external rce, acting.upon it in some way or other. I have seen a gentleman, when skaiting on very slippery ice, go a great way without any exertion to himself; but where the ice was rough, he could not go half the distance -without making fresh e orts.
FA R.-I will mention another instance or two on this law of motion. Put a bason of water into your little sister's wagon, and when the water is per­ ctly still, move the wagon, and the water, resisting the motion of the vessel, will at rst rise up in the direction contrary to that in which the vessel moves. If, when the motion of the vessel is communicated