## PHYS208 Fundamentals of Physics II

Student Inquiry:
In lecture a few days ago you mentioned 'Superpostion Theory' and referred to learning it in PHYS207, which I didn't take. I've checked with some people who had PHYS207 and they weren't sure what you meant by it either. I've also checked with the TA who thought it might be the method used to approach vector problems, but he wasn't certain. Since you indicated this was very important to the class I was hoping you could briefly explain this theory and where I can find out more about it. [9/9/97]

My response:
Referring to the earliest reference to superposition in HRW (page 324) states:

 Given a group of particles we find the net (or resultant) gravitational force exerted on any one of them by using the principle of superposition. This is a general principle that says a net effect is the sum of the individual effects. Here, the principle means that we first compute the gravitational force that acts on our selected particle due to each of the other particles, in turn. We then find the net force by adding these forces vectorially, as usual.

So the superposition principle is what allows us to add forces together to find a resultant when the forces come from different sources. You have been doing this all along in PHYS207 and have probably taken it for granted. But it is a fundamental property of the space that we live in -- consider what it might be like to live in an alternate universe where the superposition principle is not at work.

We will again be relying on the superposition principle next week when we calculate the electric field arising from a continuous distribution of charge by dividing it into infinitesimal elements and integrating over the infinitesimal contributions to the electric field that result. So it is fair to say, that without the superposition principle, calculus would be much less useful!

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"http://www.physics.udel.edu/~watson/phys208/superposition.html"
Last updated Feb. 13, 1998.
Copyright George Watson, Univ. of Delaware, 1998.