20. A railroad train weighing 400 tons has a velocity of 60 miles per hour. An ocean steamer weighing 20,000 tons has a velocity of one half mile per hour. How do their momenta compare?
21. Why is a heavy boy preferable to a lighter weight boy for a football team?
22. Why does a blacksmith when he desires to strike a heavy blow, select a heavy sledge hammer and swing it over his head?
23. Why does the catcher on a baseball team wear a padded glove?
(3) Resolution of Forces
82. Resolution of Forces.—We have been studying the effect of forces in producing motion and the results of combining forces in many ways; in the same line, in parallel lines, and in diverging lines. Another case of much interest and importance is the determination of the effectiveness of a force in a direction different from the one in which it acts. This case which is called resolution of forces is frequently used. To illustrate: one needs but to recall that a sailor uses this principle in a practical way whenever he sails his boat in any other direction than the one in which the wind is blowing, e.g., when the wind is blowing, say from the north, the boat may be driven east, west, or to any point south between the east and west and it is even possible to beat back against the wind toward the northeast or northwest. Take a sled drawn by a short rope with the force applied along the line AB (see Fig. 62); part of this force tends to lift the front of the sled as AC and a part to draw it forward as AD. Hence not all of the force applied along AB is used in drawing the sled forward. Its effectiveness is indicated by the relative size of the component AD compared to AB.
Fig. 62.—AD is the effective component.
The force of gravity acting upon a sphere that is resting on an inclined plane may be readily resolved into two components, one, the effective component, as OR, and the other, the non-effective as OS. (See Fig. 63.) If the angle ACB is 30 degrees, AB equals 1/2 of AC and OR equals 1/2 of OG, so that the speed of the sphere down the plane developed in 1 second is less than (about one-half of) the speed of a freely falling body developed in the same time. Why is OS non-effective?
