11. :: : The weak equivalence principle only applies to point particles in a gravitational field. 12. As far as we know, electrons are point particles with no intrinsic size at all. 13. Nevertheless, there is good reason that an elementary particle is often called a point particle . 14. Given some molecule, you are free to consider it as a system of point particles . 15. It is often a hypothetical simplified point particle with no properties other than mass and charge. 16. Likewise, in electromagnetism, physicists discuss a "'point charge "', a point particle with a nonzero charge. 17. This implies that the point particle would have infinite inertia, making it unable to be accelerated. 18. String theory extends ordinary particle physics by replacing zero-dimensional point particles by one-dimensional objects called strings. 19. In general relativity, geodesics describe the motion of point particles under the influence of gravity alone. 20. However unlike point particles , point mass can only apply to an object that is infinitely small.
