einstein says that travelling faster than light speed is impossible so........?

Question

if i hold a steel rod that is 1 meter long with a knob on the end and i turn 360 degrees, the knob travels at X speed.
if i extend the rod to 10 meters and urn at the same speed, the knob travels at a faster velosity.
if i extend the rod to EG. 100 trilion miles, surley the knob at the end would break light speed???? or would the rod bend??? or physics would force me to turn at a slower speed???

Answer 1

This is purely a thought experiment so you should ignore the answers that tell you you can't have a rod that long or you couldn't spin it that fast or whatever. That being said:

The rotational speed at the end of the rod will certainly increase with increasing length of a rigid shaft. And, if long enough and spun fast enough, would certainly reach speeds to infinity - relativity aside and mathematically speaking, of course.

But the same mathematics have a serious restriction as to just how fast you can get this knob going. The equation for kinetic energy is E=MC^2/sqrt[1-(v^2/C^2)]
If the velocity (V) equals the speed of light (C) the denominator becomes the square root of 1-1 or zero! If you try to exceed the speed of light, the denominator becomes the square root of a negative number - and now we're getting into some pretty shaky, unknown territory.
I don't honestly know would happen under these conditions - I would speculate, however, that the energy required to move this mass would be the limiting factor.

Answer 2

The problem with the speed of light is that our universe is defined by this speed. Einstien's equations predict that as an object approachess the speed of light it will shrink and it will become heavier. If something were to actually reach the speed of light, it would be infinetely small and infinitely heavy. However, something that is infineitely small and heavy would have infinite gravity and, thus, destroy the universe (which some people would consider undesireable). Not to mention that the heavier an object is, the more energy it will take to accelerate it. So, as you get closer to the speed of light, you would need infinite energy to accelerate the tiniest bit faster. Interestingly, the equations allow for the concept of a particle which is born traveling faster than light which could then never travel slower than the speed of light. This theoretical particle was of some interst but, eventually, proven to be impossible to exist. I'm sure you'll continue to believe that the limits of the speed of light are wrong, but that's because you are more interested in fantasy than you are in science. If you really were interested in the science of your question, you would take a Modern Physics class at your local university.

Answer 3

Yes, this is indeed an interesting thought experiment. Since it is clearly impractical, maybe consider a rigid massless rod with a knob on the end, and do the same thing again! I devised a similar thought experiment, but using a "beam" of light instead. Of course, respondents were eager to point out that a "beam" of light is in fact not "solid", so the light in the beam does not have any tangential component at all, only a radial component, which is travelling at the speed of light.

Answer 4

The motion of the far end of the rod is not instantaneous, and not faster than the speed of light. The "pulse," (essentially a compression wave), of you turning one end of the rod moves through the rod at the speed of sound in whatever material the rod is made of. The earliest that the far end of the rod could move, after you start to turn the near end, is the length of the rod divided by the speed of sound in the rod.

The speed of sound through, say, steel, is a lot faster than the speed of sound through air, but still a lot slower than the speed of light.

Answer 5

If you could apply enough torque the rod would bend.

Actually the problem pops up physics. There are neutron stars and other large objects in space that rotate extremely fast and have very strong magnetic fields. We can assume that the field lines are fixed on the surface of the object and rotate with it. As you move away from the rotating body there reaches a point where the magnetic field has to "lag behind" or it will violate relativity.

Answer 6

Physics would force you to turn at a slower speed. Try it. I mean, anyone can turn a short rod pretty fast, but have you tried to turn a long rod lately? Even a 20 foot rod is noticeably harder to turn than a 2 foot one. Imagine how hard it would be to turn that really long rod you are talking about, even without considering relativity. But relativity would still apply to the tip of the rod, making it even harder to turn.

Answer 7

Einstein's theory makes energy and mass interchangable. Therefore when an object is given kinetic energy, it does in fact weigh more. These are proportional so that you require more energy to speed the knob up even more. If the knob is travelling at the speed of light then the energy needed to speed it further becomes infinite. Therefore it is not possible. Also the speed of light is the speed of electromagnetic interaction. Simply the fastest that a change in the fabric of spacetime can occur.

Answer 8

Your knob would break off long before you attained the desired supra-luminal speed, due to the incredibly large centripetal force required, being greater than the shear strength of the material.
It would work with an extremely powerful laser though.. only problem you would not be able to transmit information at faster than light speed.
Travelling at the speed of light is impossible for material objects. There is no restrictions on faster than light travel.. make your rod from..tachyons! Or try waving your knob about in water..the speed of light in this medium is only 2.25x10^8 m/s!

Answer 9

Your real problem is that long before your knob on the end of your rod is reaching light speed or even 1000 mph the thing will become too heavy for you to lift !!!
Hypothesis therefore untestable.
Personally I think it unsound anyway....
Ah well try again

Answer 10

When i turned 360 degrees with my 7'' rod with a knob on the the end of it my nan scremed and beat me with her walking stick!