“I will try,” said Tom, as he took out his pencil and pocket-book, to make the calculation. “The momentum of the battering ram must be estimated by its weight, multiplied into the space passed over in a second of time; which is 100,000 multiplied by 20; that will give 2,000,000. Now, if this momentum, which must also be that of the cannon ball, be divided by the weight of the ball, it will give the velocity required, which I make out to be 62,500 feet.”
“Admirably calculated,” said Mr. Seymour: “and I will take care, my dear Tom, that your intelligence shall be suitably rewarded.”
Mr. Twaddleton here observed, that he thought “his young friends and playmates” must have received, for that day, as much philosophy as they could conveniently carry away without fatigue. Mr. Seymour concurred in this observation; and the more readily, as the path they had to travel was rugged, and beset with difficulties. “I will, therefore,” said he, “not impose any farther burthen upon them; but I will assist them in tying, into separate bundles, the materials which they have collected in their progress, in order that they may convey them away with greater ease and security. Know then, my dear children,” said the affectionate parent, “that you have this day been instructed in the three great Laws of Motion, viz.
I. That every body will continue in a state of rest, until put into motion by some external force applied to it, and if that force be single, the motion so produced will be rectilinear, i.e. in the direction of a straight line.
II. Change of motion is always proportional to the moving force impressed, and is always made in the direction of the right line in which the force acts.
III. Action and Reaction are equal in equal quantities of matter, and act in contrary directions to each other.”
CHAPTER IV.
A sad accident turned to a good account.--One example worth a hundred precepts.--The Centres of Magnitude and Gravity.--The Point of Suspension.--The Line of Direction.--The stability of bodies, and upon what it depends.--Method of finding the centre of gravity of a body.--The art of the Balancer explained and illustrated.--Various balancing toys.