Bang! Boing! Pop! Interactive Physics on the World Wide Web
Created for Thinkquest 96 by Josh Levine, Paulina Kuo, and Doug Brown
The ideas of the story of the security guard and the office building can be applied to energy, linear momentum and angular momentum. The key point is that the total amount of each of these three quantities will stay the same in an isolated system if you are able to count up each quantity accurately, even though the locations and forms may change. Just as the people in the board meeting were invisible to the security guard, sometimes the quantities will seem to disappear. In this situation, one must find a different way to detect and measure what is really there; with the board room, the security guard was able to detect the people by measuring the temperature change.