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Re: [Phys-l] pseudo-force



In your thought experiment, you turn the normal force exerted upward on
the person by the chair on and off at the same time that you turn the
gravitational force exerted on the person on and off. How can you tell
whether you are feeling the gravitational force or the normal force?
Let's put the person in the chair in outer space far from any stars or
planets. Let's bring the floor along and have the chair bolted to it.
Now turn the gravitational force on and off (perhaps by having a planet
"below the person" come into and out of existence). (Make the
gravitational field close enough to being uniform that tidal forces are
negligible.) I don't think the person would be able to feel that the
gravitational field is being turned on and off.

Now, instead of turning the gravitational field on and off while keeping
the normal force off, suppose we turned the normal force on and off
while keeping the gravitational force turned off. This could actually
be realized by attaching some rocket engines to the floor. The person
would definitely feel the normal force being turned on and off.

(Note: I agree strongly with folks who say that, if tidal forces are
strong enough, we can feel tidal forces. The tidal forces exerted by the
earth on a person near the surface of the earth, in terms of what the
person feels, are, however, negligible.)

Mike Edmiston wrote:

... That is, if there were a gravity switch, and you strapped me to a
chair bolted to earth, and then you turn gravity on and off, I could
sense the difference between off and on. And I wouldn't only sense the
difference in my butt. I would sense it all over.

I realize you can still call this a particular viewpoint. But if a
person could sit there and sense gravity being turned on an off, any
person in their right mind would say they were sensing gravity.