Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Is the room moving?

Learn more physics!

Most recent answer: 01/22/2013
Q:
You awaken inside a room with no windows or doors. You want to know if the room you are in is moving within some vehicle or at rest relative to the earth's surface. How can you find out?
- Dominick Bonito (age 58)
West Haven , CT. USA
A:

If this occurred in space with no influence of any kind of external force, the person trapped inside the room would  have no way of knowing whether he is at rest with some particular frame or moving at a constant velocity in respect to it. In your scenario, however, we have some effects from the nearby Earth.

You could measure the direction of the magnetic field with a compass and then check to see if there's an electric field at right angles to it.That would be there if you're moving with respect to the Earth, so long as the motion is not directly along the magnetic field direction. 

If you are really moving along with the Earth's surface, that's actually a non-inertial frame, due to the Earth's rotation. The Coriolis force will be measurable, with some care.  The centrifugal effects will slightly change the effective gravitational constant, so if you happen to know the exact weight of something in the Earth-surface frame, you could look for tiny changes compared to that.

cfzhang


(published on 01/22/2013)

Follow-up on this answer.