How many different kinds of force would act on a proton if placed in both an electric field and a gravitational field?

Answer 1

This is actually a more complicated question than at first it would seem. If placed in an electric field the proton would experience both electric and magnetic forces as these are actually two parts of the one force, the electromagnetic force. Including the gravitational field that would seem to make three. However, the proton would actually experience all the other fundamental forces of nature, the weak and strong nuclear interactions as these permeate all space. In essence, since electromagnetism is usually counted as one force, the proton would experience four forces. p.s.: Theories invented over the past few decades have amalgamated some of these forces into single interactions, namely the electroweak interaction - electromagnetism and weak nuclear force. This might even go further so that in the end we may talk of only one fundamental force. Keep it simple. The forces acting on the proton are the electromagnetic force and the gravitational force. As so astutely pointed out above, the electric and magnetic forces are represented by the electromagnetic force. Gravity is a no-brainer here; the force will act on the proton as well. As regards the weak and strong interactions, and the electroweak force, which has a carrier (a particle) combining the electromagnetic and weak forces, and the proposed fundamental force, they are not "part" of this question, really. It's a simple question, and there are implications extant because we're talking quantum mechanics. But why complicate things? There is no compelling reason to do so. There will be time enough to look at the other forces mentioned. And since they were not mentioned here in the question, and there is nothing else that would give rise to the in the situation cited, we can "skate by" the other ideas. We can then address them when another particle enters the picture, or when some other variable is added to the situation.

Answer 2

A proton in an electric field would experience an electric force due to its charge, and in a gravitational field it would experience a gravitational force due to its mass. So, there would be two different kinds of forces acting on the proton: electric force and gravitational force.