Thought experiment, a really long lever

Aerozord · 01-13-2012, 06:47 PM

so last night I was thinking of the quote "give me a long enough lever and I will move the world" and went, what if you did have a really long lever.

This led me to the following thought experiment

You have a lever thats, lets say 100 million lightyears long, and made of a perfect solid that doesn't bend or brake. Fulcrum at one end and force applied directly above it. You have nigh-limitless force to apply to it.

Now what would happen? Because of the length even an incredibly minute amount of acceleration would cause the other end to break the lightspeed barrier. Made me wonder if there is a minimum amount of force required to break inertia, and if so would that make the lever immovable in this manner do to limit on acceleration at the other end?

Other is what kind of odd effect that would have on the center of gravity and equation for a lever, since the kinetic energy would increase exponentially and center of gravity would change due to the changes in mass. In fact would it be an instantaneous or a progressive change?

Amake · 01-13-2012, 06:57 PM

My immediate thought is, there's going to be some odd bendy effects along the lever as it approaches the speed of light. It should get weird within just one light year of the fulcrum as we remember the movement of the lever can only propagate from one end to the other at the speed of light. To accommodate an unbendable lever I imagine space will have to bend around it somehow.

Interesting idea. I'm a little sleep deprived to consider it further right now though.

Mr.Bookworm · 01-13-2012, 07:24 PM

Quote:

Originally Posted by Aerozord

Now what would happen? Because of the length even an incredibly minute amount of acceleration would cause the other end to break the lightspeed barrier.

No, it wouldn't. The speed of light in a vacuum (c) is an absolute. You would get a lever going some enormous fraction of c, but you would never reach c (doing so requires infinite force). You would need more and more force to move the lever as it approaches c.

On what actually happens to the lever, you get weird time shit on the other end, and it becomes really fucking heavy at the other end. Of course, it takes you 100 million years to see it happening.

Quote:

Made me wonder if there is a minimum amount of force required to break inertia, and if so would that make the lever immovable in this manner do to limit on acceleration at the other end?

Uh. What. No, you can't "break" inertia. You would need an increasing amount of force to move the lever, due to the lever's increasing mass as it approaches c.

Sithdarth · 01-13-2012, 07:41 PM

The existence of said lever requires that the bonds between the atoms in said lever be of infinite strength. Thus the question is meaningless because the assumptions you have to make to allow for the existence of the lever, perfect rigidity, directly alter the properties you are attempting to explore, the motion of the lever. Such thought experiments are absolutely useless because you can't accurately explore a set of properties while simultaneously postulating an impossibility that effects those properties.

Aerozord · 01-14-2012, 12:27 AM

Quote:

Originally Posted by Sithdarth

The existence of said lever requires that the bonds between the atoms in said lever be of infinite strength. Thus the question is meaningless because the assumptions you have to make to allow for the existence of the lever, perfect rigidity, directly alter the properties you are attempting to explore, the motion of the lever. Such thought experiments are absolutely useless because you can't accurately explore a set of properties while simultaneously postulating an impossibility that effects those properties.

ok, then what if it wasn't perfectly rigid, would the forces just rip it apart?

Sithdarth · 01-14-2012, 12:41 AM

Pretty much. I'd wager it's own weight would probably rip it apart. But it was actually mathematically proven that in Relativity there can be no such thing as a rotating rigid object at relativistic speeds. Relativistic effects make it impossible.

Seil · 01-14-2012, 01:17 AM

I thought it was just a figure of speech.

Sithdarth · 01-14-2012, 01:44 AM

This is for a dis but the same arguments apply for really any rotating object such as a lever.

01-13-2012, 06:47 PM	#1
Aerozord So we are clear Join Date: Jan 2004 Location: Former murder capital of the world Posts: 13,824	Thought experiment, a really long lever so last night I was thinking of the quote "give me a long enough lever and I will move the world" and went, what if you did have a really long lever. This led me to the following thought experiment You have a lever thats, lets say 100 million lightyears long, and made of a perfect solid that doesn't bend or brake. Fulcrum at one end and force applied directly above it. You have nigh-limitless force to apply to it. Now what would happen? Because of the length even an incredibly minute amount of acceleration would cause the other end to break the lightspeed barrier. Made me wonder if there is a minimum amount of force required to break inertia, and if so would that make the lever immovable in this manner do to limit on acceleration at the other end? Other is what kind of odd effect that would have on the center of gravity and equation for a lever, since the kinetic energy would increase exponentially and center of gravity would change due to the changes in mass. In fact would it be an instantaneous or a progressive change? __________________ "don't hate me for being a heterosexual white guy disparaging slacktivism, hate me for all those murders I've done."

01-13-2012, 06:57 PM	#2
Amake Keeper of the new Join Date: Apr 2004 Location: A place without judgment Posts: 4,506	My immediate thought is, there's going to be some odd bendy effects along the lever as it approaches the speed of light. It should get weird within just one light year of the fulcrum as we remember the movement of the lever can only propagate from one end to the other at the speed of light. To accommodate an unbendable lever I imagine space will have to bend around it somehow. Interesting idea. I'm a little sleep deprived to consider it further right now though. __________________ Hope insistent, trust implicit, love inherent, life immersed

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01-13-2012, 07:41 PM	#4
Sithdarth Friendly Neighborhood Quantum Hobo Join Date: Mar 2004 Location: Outside the M-brane look'n in Posts: 5,403	The existence of said lever requires that the bonds between the atoms in said lever be of infinite strength. Thus the question is meaningless because the assumptions you have to make to allow for the existence of the lever, perfect rigidity, directly alter the properties you are attempting to explore, the motion of the lever. Such thought experiments are absolutely useless because you can't accurately explore a set of properties while simultaneously postulating an impossibility that effects those properties.

01-14-2012, 12:41 AM	#6
Sithdarth Friendly Neighborhood Quantum Hobo Join Date: Mar 2004 Location: Outside the M-brane look'n in Posts: 5,403	Pretty much. I'd wager it's own weight would probably rip it apart. But it was actually mathematically proven that in Relativity there can be no such thing as a rotating rigid object at relativistic speeds. Relativistic effects make it impossible.

01-14-2012, 01:17 AM	#7
Seil Super stressed! Join Date: Feb 2007 Location: British Columbia Posts: 8,081	I thought it was just a figure of speech.

01-14-2012, 01:44 AM	#8
Sithdarth Friendly Neighborhood Quantum Hobo Join Date: Mar 2004 Location: Outside the M-brane look'n in Posts: 5,403	This is for a dis but the same arguments apply for really any rotating object such as a lever.