How Everything Works
How Everything Works How Everything Works

Question 1218

I think that the speed of light could be broken by turning a very long lever. If the lever is long enough and you have enough power to turn it, the end of the lever will travel faster than the speed of light. Is this so? — NL, Hong Kong
I'm afraid that this technique won't work—the torque you would have to exert on the lever to make its end approach the speed of light would become infinite and the energy you would have to transfer to the lever would also become infinite. The Newtonian laws of motion aren't accurate at such high speeds and the full relativistic laws are required. With this shift to relativistic motion come changes in the relationship between force and acceleration, and between torque and angular acceleration. The faster the end of the lever moves, the harder it is to increase its speed any further. As the lever tip approaches the speed of light, it becomes essentially impossible to make it move faster.

As if this problem weren't enough, there is another problem: if you aren't extremely patient, the lever will bend as you turn it, forming a spiral rather than a long arm that sweeps through space. That's because the lever is kept straight by internal forces. While you are twisting the lever to make it turn faster, you are unbalancing these internal forces and causing the lever to bend. The long lever you describe will actually curl into a spiral and its end speed will never come close to the speed of light.


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