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Energy, Work, and Power

GED Science Practice Test: Work

Work is a word that people have an intuitive understanding of. When you place several heavy boxes on a high shelf, you understand that you’ve done a lot of work.  In physics, something (or someone) is said to do work when it applies a force to move or displace an object over a distance.  Thus, in the above example, you applied a force to the box and box moved over a distance.  Work is represented by the following formula:

If you remember from the previous physics lesson, force is measured in Newtons, and distance is measured in meters.  Thus, the unit for work is a Newton-meter, called a Joule (J).

While work is intuitively understood, there is something about work that can be confusing.  Imagine that you push really, really hard on a wall for about one minute.  You may think that you did a lot of work, but in reality, you did zero work!!!   If you examine the formula above, you will understand why.  You applied a great deal of force, but did not move the wall.  So you multiply that large amount of force by zero, and as a result, you have done zero work on the wall.

Another somewhat confusing thing about work is that the force applied has to be in the direction of the displacement.  What this means is that if you carry a box across a room, you are not doing any work on the box.  Because your force is pushing upward on the box (you serve to keep the box up off the floor), and the displacement is left to right across the room, no work is done—your force is perpendicular to the box. The following image shows these two unintuitive examples showing no work being done:

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