Intermediate physics / by W. Watson.

  • Watson, W. (William), 1868-1919.
Date:
1912
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Licence: In copyright

Credit: Intermediate physics / by W. Watson. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    PHYSICS CHAPTER I DISPLACEMENT 1. Position.—In order to specify the position of a point on a plane surface, such as a sheet of paper, we may give its perpendicular distance from two intersecting reference lines drawn on the surface. Although it is not essential, it is in general convenient to take the reference lines, or axes as they are called, at right angles, when we are said to use rectangular co-ordinates. The distances of the point from the axes are called the co-ordinates of the point, and when we know the position of the axes and the or^nates co-ordinates of a point we can immediately locate the point. Thus suppose we take the left-hand and bottom edges of a sheet of paper as the axes and are given that the distance of a point from the lower edge is 3 inches and the distance from the left-hand edge is 4*5 inches; then if we draw a line parallel to the lower edge and at a distance of 3 inches, it is obvious that the given j^oint must lie somewhere- in this line. In the same way if we draw a line parallel to the left-hand edge and at a distance q , of 45 inches from it, the point must lie on this line. Hence the point must be at the only point which is common X' | ^ j.' X' to the two lines, that is at their inter- section. Further, it is evident that there can be only one point which R* has the given co-ordinates. If xox' and yoy' (Fig. 1) are the CO ordinate axes, the co-ordinates of a point p are cm and on, the co-ordinate om being called the abscissa of the point p and on the ordinate. A common convention is to use the letter x to indicate the abscissa of a point and the letter y to indicate the A N Y'