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Re: Frames of Reference



Does the physicist, checking for momentum conservation in a bubble chamber
photograph, worry about the earth providing a moving frame of reference
or do they operate as we do in a conventional lab, assume the lab is an
inertial frame?

He doesn't have to. The quantity which is important in collisions is the
impulse exchanged. These interactions take place over such a short time
that any impulse due to gravitational forces is utterly unobservable,
though the gravitational forces are in principle quite observable.

That's a good problem to give your students, however. Many will say "The
gravitational force is just too small to matter". That is not the case, of
course. If the particles stuck around for a tenth of a second in the spark
chamber they would fall just as far as a tennis ball in the same time. The
question will test whether or not they are thinking.

Leigh