Physics and Force Help
Introduction to Force
Imagine again that you are in a spacecraft orbiting the Earth, so everything in the cabin is weightless. Two objects float in front of you: a brick and a marble. You know that the brick is more massive than the marble. However, either the brick or the marble can be made to move across the cabin if you give it a push.
Suppose that you flick your finger against the marble. It flies across the cabin and bounces off the wall. Then you flick your finger just as hard (no more, no less) against the brick. The brick takes several minutes to float across the cabin and bump into the opposite wall. The flicking of your finger imparts a force to the marble or the brick for a moment, but that force has a different effect on the brick than on the marble.
Force As A Vector
Force is a vector quantity. It can have any magnitude, from the flick of a finger to a swift leg kick, the explosion of powder in a cannon, or the thrust of a rocket engine. Force always has a defined direction as well. You can fire a pop-gun in any direction you want (and bear the consequences if you make a bad choice). Vectors are commonly symbolized using boldface letters of the alphabet. A force vector, for example, can be denoted by the uppercase boldface letter F .
Sometimes the direction of a force is not important. In such instances, we can speak of the magnitude of a force vector and denote it as an uppercase italicized letter F . The standard international unit of force magnitude is the newton (N), which is the equivalent of a kilogram-meter per second squared (kg · m/s 2 ). Suppose that the brick in your spacecraft has a mass of 1 kg and that you push against it with a force of 1 N for 1 s and then let go. The brick will then be traveling at a speed of 1 m/s. It will have gone from stationary (with respect to its surroundings) to a speed of 1 m/s, which might seem rather slow unless it hits someone.
How Force Is Determined
Force can be measured by the effect it has on an object with mass. It also can be measured by the amount of deflection or distortion it produces in an elastic object such as a spring. The “mass meter” described earlier for determining mass can be modified to make a “force meter” if one-half of it is taken away and a calibrated scale is placed alongside (Fig. 7-4). This scale must be calibrated in advance in a laboratory environment.
Fig. 7.4 . A “force meter.”
Practice problems of these concepts can be found at: Mass, Force, And Motion Practice Test
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