Relativistic effects on a body rotating at near c

[dan_r]

Hi all, I've just been thinking about something today which I freely admit I've not got the knowledge to actually comprehend at this time (my physics studies don't start until September!) and so it might actually belong in engineering or it might just be a load of nonsense that I've gotten wrong!

If I were to set up an apparatus and attach a little model spaceship to it, which extended around, say 10m from the apparatus. Could I then, given the correct amount of energy input, rotate the apparatus at such a speed whereby the little model spaceship could achieve a velocity close to c.. and if so, would we start seeing relativistic effects occurring around the spaceship and apparatus as well?

So you're not actually achieving such speeds through direct velocity sending something in a straight line, but through the inertial effect on an extended body from the apparatus.. would that lower the energy demands of reaching such velocity if the extended body were constructed as to be able to withstand the rigours of such speeds?

 

[HallsofIvy]

I am not at all sure what you are asking here. The kinetic energy in an object moving at speed v is the same whether it is moving in a straight line or circle. The energy necessary to get it to that speed is the same in either situation.

 

[dan_r]

Hi, sorry it is a bit unclear.

It could be better described as the level of acceleration around a pivot. In my head I'm imagining it as being almost like a lever, whereby you can generate higher velocity with a much reduced input of energy?

I'll draw a diagram when I get home to my PC; I'm terrible at trying to explain what I can see in my mind!

 

[danR]

Hi, sorry it is a bit unclear.

It could be better described as the level of acceleration around a pivot. In my head I'm imagining it as being almost like a lever, whereby you can generate higher velocity with a much reduced input of energy?

I'll draw a diagram when I get home to my PC; I'm terrible at trying to explain what I can see in my mind!

With a fixed mass, the same velocity needs the same energy. Anything else, and you could build a perpetual motion machine. But if you can, then you are a very rich man.

--the other danR

 

[dan_r]

With a fixed mass, the same velocity needs the same energy. Anything else, and you could build a perpetual motion machine. But if you can, then you are a very rich man.

--the other danR

Haha, very rich indeed! Good to see us Dan Rs get around though!

I think I'm understanding where I'm going wrong with this idea now; I was getting the impression that the inertia would drive the extended item to move at a higher velocity than the pivot around which it spun, because obviously it stays equidistant from the pivot, but covers a longer distance.

In my head I was thinking that the pivot could spin at x but the item would travel at y because of this.. it's a bit like a mental illusion I suppose. Got a lot to learn!

 

[cowmoo32]

Well, it would have a higher angular velocity than the pivot point, you're correct there.

 

[dan_r]

Well, it would have a higher angular velocity than the pivot point, you're correct there.

Ah good! My brain WAS working then!

Ok, with that info, I've found this thread on search which might be of interest to people who've followed the thread:

https://www.physicsforums.com/showthread.php?t=14176

It seems that you would reach a point where the body spinning around the axis would acquire so much mass that it would start to slow down the mechanism of rotation hence slowing down itself.