Can a rotating rod exceed the speed of light?

  • Thread starter T-O7
  • Start date
  • Tags
    Rod
In summary, the conversation discusses the possibility of a rod rotating at a speed that would cause the far end to move faster than the speed of light. It is determined that this is not possible due to the limitations of material rigidity and the propagation of force through the rod.
  • #1
T-O7
55
0
Hey,

There's one thought experiment that I can't seem to wrap my head around.

If we had an extremely long rod (say > 1 lightsecond) and rotate it about one end rapidly enough (say 1 rad/second), would the far end of the rod be moving faster than the speed of light (using v=omega*r)?

What's going on?
 
Physics news on Phys.org
  • #2
What makes you think you could get it up to that speed of rotation?

Consider the last inch of the rod like a little spaceship. It still has mass and inertia. The force applied to it (whether from a rocket exhaust or from a radial force 1/2 light second away) still experiences the same inertia. At some point in gearing up your rotation, you simply would not be able to accelerate the rotation any more.

Also, consider that there is no such thinbg as a rigid material. The force applied at any point on the rod can only be propogated through the material of the rod at a limited speed (significantly less than c). The rod will bend, even if it is an "ideal" material. Eventually, you will have an s-shaped rod one light-second in length. The ends will not be rotating as fast as the centre.
 
  • #3
Ah OK, I see.
Thanks a lot! :smile:
 

What is a really really long rod?

A really really long rod is a cylindrical object with an elongated shape that is significantly longer than its diameter. It is commonly used in various industries for structural support, transmission of energy, and measurement purposes.

What materials are used to make a really really long rod?

The materials used to make a really really long rod vary depending on its intended use. Some common materials include metal alloys, such as steel or aluminum, as well as composite materials like carbon fiber. The material chosen will depend on factors such as strength, weight, and durability.

What are the potential applications of a really really long rod?

A really really long rod has a wide range of potential applications. It can be used as a structural support in buildings and bridges, as a conductor for electrical energy, as a measuring tool in surveying and construction, and even as a tool for fishing or hunting.

How is the length of a really really long rod measured?

The length of a really really long rod is typically measured in units such as meters, feet, or inches. In scientific research, more precise measurements may be made using specialized instruments such as calipers or laser distance meters.

Can a really really long rod break or bend?

Yes, a really really long rod can break or bend depending on its material and the amount of force applied to it. For example, a metal rod may bend under excessive weight or pressure, while a carbon fiber rod may break if it is exposed to extreme temperatures. Proper use and maintenance can help prevent these types of damage.

Similar threads

I Relativity's Effect on Long Rod Shape and Speed
    • Special and General Relativity
Replies
11
Views
1K
A Electrodynamics of moving bodies - §2: On the relativity of... (again)
    • Special and General Relativity
2
Replies
35
Views
2K
A Stress-energy tensor of a rotating rod
    • Special and General Relativity
Replies
21
Views
2K
I Is it feasible to measure one way speed of light this way?
    • Special and General Relativity
2
Replies
52
Views
4K
I Time & Gravity in Rotating Faster Than Light?
    • Special and General Relativity
Replies
8
Views
1K
I What Causes the Einstein - de Haas Effect in Iron Rods?
    • Other Physics Topics
2
Replies
39
Views
1K
B Can an Object Exceed the Speed of Light?
    • Special and General Relativity
Replies
12
Views
1K
I How specifically does an accelerated uniform rod Lorentz contract?
    • Special and General Relativity
2
Replies
55
Views
3K
I Measuring One-Way Anisotropy of Light Speed
    • Special and General Relativity
Replies
2
Views
1K
I Relative Speed of Light Between Objects
    • Special and General Relativity
Replies
3
Views
949

Hot Threads

Recent Insights

Back
Top