Is It Electric or Magnetic? Depends on Where You Stand

If you took introductory physics, you learned about the “fundamental forces.” It goes something like this: All interactions are the result of one or more of five basic forces: strong nuclear, weak nuclear, gravity, electric, and magnetic. “Doing physics,” then, means identifying the forces in play.

There’s a problem, though, which might not have been mentioned: The forces you observe depend on your vantage point—your “frame of reference.” Look out the window. Trees, houses, lawns—they’re all stationary, right? But look at that same spot from space and it’s moving a thousand miles an hour. It looked still to you before because you were moving with it.

We have this same problem with electric and magnetic fields. Depending on your reference frame, what appears to be a magnetic force from one spot appears to be an electric force from another.

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