A manual of physics, theoretical and practical : for medical students / by Hugh C. H. Candy.

  • Candy, Hugh Charles Herbert, 1859-1935.
Date:
1918
Catalogue details

Licence: In copyright

Credit: A manual of physics, theoretical and practical : for medical students / by Hugh C. H. Candy. Source: Wellcome Collection.

    33/470 (page 19)
    Sir Isaac Newton (b. 1642, d. 1727) clearly recog¬ nized tliat tlie cause of motion is force. His famous “ Laws of Motion ” were first published, in Latin, in 1687. The first law of motion may be literally translated thus :— Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by impressed force. This statement recognizes that matter possesses a property, inertia, which tends to preserve the status quo by opposing, as it were, a passive resist¬ ance to any disturbance of this. Newton regarded the statement as an axiom : (T) if a body be at rest it will remain at rest unless some force acts on it ; if in motion, the velocity of motion must continue uniform unless some force causes it to increase or diminish ; (2) the direction of motion must continue unchanged, and therefore rectilinear, unless some, force cause it to be diverted. This law, therefore, supplies us with a definition of force which is often expressed as follows :— Force is that which produces, or tends to pro¬ duce, motion or change of motion. The second law of motion mav be translated as follows :— The change of motion (produced) is proportional to the impressed force producing it, and pursues the direction in which that force is impressed. This law leads to a method of measuring forces. When we change the velocity with which a mass is moving, we also change its momentum (p. 12). The change in the momentum will serve to measure the