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Ferguson's Lectures on Select Subjects, in Mechanics [
Ferguson's Lectures on Select Subjects in Mechanics Author:James Ferguson General Books publication date: 2009 Original publication date: 1805 Notes: This is a black and white OCR reprint of the original. It has no illustrations and there may be typos or missing text. When you buy the General Books edition of this book you get free trial access to Million-Books.com where you can select from more than a million book... more »s for free. Excerpt: LECTURE III. 0F THE MECHANICAL P0WERS. If we consider bodies in motion, and compare The them together, we may do this either with re- tionfaii , . c mechanics. spect to the quantities or matter they contain, or the velocities with which they are moved. The heavier any body is, the greater is the power required either to move it or to stop its motion; and again, the swifter it moves, the greater is its force. So that the whole momentum or quantity of force of a moving body is the result of its quantity of matter multiplied by the velocity with which it is moved ; and when the products arising from the multiplication of the particular quantities of matter in any two bodies by their respective velocities are equal, the momenta or entire forces are so too. Thus, suppose a body, which we shall call A, to weigh 40 pounds, and to move at the rate of two miles in a minute; and another body, which we shall call B, to weigh only four pounds, and to move 20 miles in a minute; , the entire forces with which these two bodies would strike against any obstacle would be equal to each other, and therefore it would require equal powers to stop them : for 40 multiplied by 2 gives 80, the force of the body A; and 20 multiplied by 4 gives 80, the force of the body B. Upon this easy principle depends the whole of mechanics: and it holds universally true, that when two bodies are suspended on any machine, so as to act contrary to each other, if the machine be put into motion, and the perpendicular assent f one body multiplied into its weight, be equal to the perpendicular descent of the other body multiplied into its w...« less