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The Graphical Representation and Composition of Velocities

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-61

2025-11-02

367

Any velocity of which the starting point, the rate, and the direction are known can be represented graphically by a vector line.

If the directions of two component velocities are in the same straight line, the resultant velocity is either the sum or the difference of the two velocities. A person walking through a railway train from the rear to the front has a greater velocity with respect to the earth than a person sitting in seat, while a person walking from the front to the rear has a smaller velocity.

FIG.1

If the directions of two component velocities are not in one straight line, the resultant velocity can be found by combining the velocities as forces are combined in the parallelogram of forces. For example, if a man rows a boat across a stream with a uniform velocity of 2 miles per hour while the stream flows with a uniform velocity of 1.5 miles per hour, the direction taken by the boat will be determined by these velocities independently of the width of the stream. If the boat starts from A, Fig. 1, the direction of the path will be found by laying off AB to represent the velocity of 2 miles per hour and AC at a right angle to it to represent a velocity of 1.5 miles per hour; then AD will be the direction the boat will take. If the width, AE, of the stream is known, the length of the path, AF, is easily determined.