18. When football players run into each other which one is thrown the harder? Why? 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_. [Illustration: 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? [Illustration: FIG. 63.--The effective component is _OR_.] [Illustration: FIG. 64.--Resolution of the forces acting on an aeroplane.]