I seem to be answering a lot of questions about basic ideas in physics. I get the impression that a lot of these come from people with no physics background who may have seen something on a TV science show and want to know a bit more.
I'm happy to answer these as I'm keen to encourage interest in physics and likewise to avoid discouraging it. But I wonder how appropriate such questions are for this
forum site, and if we need a tag to distinguish such questions.