Chapter 5: Applications of the Laws of Force and Motion

(Press the TAB key to position the cursor at the beginning of the first blank and type what you believe completes the thought. Then press the TAB key for feedback and to move to the next blank. If you miss it, delete all of the word by positioning the cursor with the mouse and backspacing over all of the letters and try again. You should be able to complete this exercise without error before completing this chapter.)

If you drop a ball from rest near the surface of the earth, its motion is accelerated. The acceleration has a value of (number, two significant digits?) kilometers per hour each second. If you throw a ball upward near the surface of the earth, its motion is (uniform, accelerated?) . The acceleration has a value of (number?) kilometers per hour each second and is directed (upward, downward?) . If you throw a ball sideways near the surface of the earth, its motion is (uniform, accelerated?) . The net force is directed (upward, downward, neither?) . If a bullet is fired perfectly horizontal from a high-powered rifle while another bullet is dropped from rest at the same height where the first is fired, the two hit the ground at (the same, different?) time. It (does, does not?) matter if a ball of different mass than the bullet is dropped. The moon moves around the earth in a circular orbit. The motion of the moon about the earth is (uniform, accelerated?) motion. This means that the force or forces on the moon are (balanced, unbalanced?) . The only significant force on the moon causing its accelerated motion is the force of . When we try to understand the motion of an object, we identify the forces on the object. Forces on other objects, such as the force exerted on the earth by the moon, are irrelevant. Forces that appear to result from physical touching are called forces. They are in reality (which fundamental?) forces and are exerted without touching. They arise from the forces of attraction and repulsion that charged particles have for one another when separated by a distance. To understand motion in terms of Newton's Laws of Motion requires a change in the way people think. Experience and educational research both show that people will cling to explanations of motion that seem "reasonable" to themselves, but which have been known to be wrong for some three hundred years. Among other things, one must think in terms of forces. Here is a recipe for identifying the significant forces on an object: 1. Choose and isolate in your mind the whose motion is of interest. Represent the object by a circle. 2. Is there a significant gravitational force on the object? Represent the force with an arrow. 3. Is there a significant electromagnetic force on the object because it is a charged object and there are other charged objects in the vicinity? Represent the force with an arrow. 4. Is there a significant force because of something your object touches? Represent the force with an arrow.

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