A scientist is completely isolated inside a smooth moving box that travels a straight-line path through space, and another scientist is completely isolated in another box that is spinning smoothly in space. Each scientist may have all the scientific goodies she likes in her box for the purpose of detecting her motion in space. The scientist in the:
a) traveling box can detect her motion.
b) spinning box can detect her motion.
c) ...both can detect their motions.
d) ...neither can detect their motions.
2007-09-13 14:49:04 · 3 answers · asked by ? 6 in Science & Mathematics ➔ Physics
The answer is indeed b. This question is the rotational counterpart to INERTIA. If your non-spinning box is moving smoothly in a straight-line path through space, you cannot sense its motion. For example, if you drop a coin above a cup it will fall directly into the cup whether or not your box is moving. Try it in a uniformly moving train or airplane. But if the box stops or starts or turns or jerks, you can sense motion. If the box accelerates you know that you're moving -- but if it doesn't accelerate you can't tell. Do all the physics experiments that you care to in your uniformly and linearly moving box and you still can't tell. Even look outside and witness a moving background and you can't say for sure whether you or the background is moving. All you can say is you are moving relative to the background, or equivalently, vice versa. Linear motion is relative.
But the spinning box is different. you know you're moving without consulting any background, and if the spin rate is...
2007-09-14 16:07:14 · update #1
...fast enough you need only consult your stomach (have you ever become nauseous on a rotating carnival ride?). And if your box is spinning very slowly you can still tell by watching the precession of a swinging pendulum. Rotational motion is absolute.
Among all the motions you can imagine, why is linear special in nature?
Why is one type of motion relative and the other absolute? Why are not both either relative or absolute? Or why not vice versa? After all, according to the ancient Greeks, circular motion is most preferred by the gods. These are deep and unanswered questions. All we know is that in our universe linear motion is relative and rotational motion is absolute. Were this not so the laws of motion would be very unlike those we live with now. But that does not explain why things are the way they are. That which is far away and exceedingly deep -- who can find it out? Pehaps you!
2007-09-14 16:12:42 · update #2
The qualified answer is b. Spin is an accelerated motion. Acceleration = Force/mass. The person in the spinning box will detect the force caused by the acceleration but she will not be able to determine the speed she's travelling through space.
2007-09-13 15:37:36 · answer #1 · answered by Anonymous · 0⤊ 0⤋
b-the sscientist in the spinning box can detect her motion.
according to the general theory of relativity, a person can't tell of he/she/it is in motion or not; as long as the motion is uniform. For acceleration, it is a different story.
Since the other scientist is in a spinning box, she is undergoing constant acceleration.
But overall, it is impossible to detect constant motion.
2007-09-13 15:40:59 · answer #2 · answered by Danny 4 · 0⤊ 0⤋
b., for reasons stated in the other answers. And she can determine her rate and direction of rotation. The rate is easy; centripetal acceleration = w^2*r. For the direction, she takes out her gyroscope, spins it up, and observes the precession of the gyroscope.. Knowing the spin and precession direction she can use the right-hand rule to deduce her rotation direction.
2007-09-14 00:39:58 · answer #3 · answered by kirchwey 7 · 0⤊ 0⤋