# The Naked Scientists Forum

### Author Topic: If I Move A Stick A light Year Long Will Both Ends Move At The Same Time ?  (Read 5234 times)

#### neilep

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##### If I Move A Stick A light Year Long Will Both Ends Move At The Same Time ?
« on: 19/06/2010 13:35:57 »
Dearest Stickologists,

As a sheepy I of course Luff sticks. Sticks are my all time favourite sticky things that are made from wood and are called sticks.

Look, here's me holding a stick just moments ago

Me Holding A Stick Just Moments Ago

Nice eh ?...will be used to incessantly prod my neighbour at 3am next Tuesday !

Now then, my stick is a good few inches in length and if I push one end I know the entire stick and both ends will move too at the same time

But say my stick is a mile long ?...100 miles ?..or how about a light year long ?...If I move my light year stick an inch forward will the other end a light year away also move an inch forward at the exact same time ?

Please ignore things like ' feasibility'...As a firm believer in empirical study I will conduct a test next Tuesday at 3am with my neighbours full co-operation.....In the mean time...whajafink ?...cos I really want to know this and I do not know and ewe may know and if ewe do know ewe can tell me so that I can know too..

hugs and shmishes

mwah mwah mwah

neil
I Haz Stick
xxxxxxxxxxxx

#### graham.d

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##### If I Move A Stick A light Year Long Will Both Ends Move At The Same Time ?
« Reply #1 on: 19/06/2010 22:48:00 »
The answer is no for lots of reasons. First of all, to move the ends of the stick a compression wave has to move along the stick from the point at which you are holding it to either end. This will be at the speed of sound in the material of the stick. If you are holding the stick in the middle, you may perceive the movement of each end of the stick to be starting at the same time. However this is only from your perspective. From anyone moving with respect to you, the ends would, generally, not start moving at the same time, though there can be positions where the two events would seem to be simultaneous. The whole concept of simultaneity is not meaningful within special relativity unless observers are in a priveleged frame of reference.

#### neilep

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##### If I Move A Stick A light Year Long Will Both Ends Move At The Same Time ?
« Reply #2 on: 20/06/2010 11:16:36 »
The answer is no for lots of reasons. First of all, to move the ends of the stick a compression wave has to move along the stick from the point at which you are holding it to either end. This will be at the speed of sound in the material of the stick. If you are holding the stick in the middle, you may perceive the movement of each end of the stick to be starting at the same time. However this is only from your perspective. From anyone moving with respect to you, the ends would, generally, not start moving at the same time, though there can be positions where the two events would seem to be simultaneous. The whole concept of simultaneity is not meaningful within special relativity unless observers are in a priveleged frame of reference.

Thank ewe very very much Graham. So, what ever the material of the stick a compression wave must first travel through it. Yes, yes...when it's elevated to such a distance I can understand it now. On such a small scale as regular stick it's something that I just would never has thought about.

#### Geezer

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##### If I Move A Stick A light Year Long Will Both Ends Move At The Same Time ?
« Reply #3 on: 20/06/2010 20:16:30 »
Neil,

Have you considered using the stick as a humane weedkiller?

#### neilep

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##### If I Move A Stick A light Year Long Will Both Ends Move At The Same Time ?
« Reply #4 on: 20/06/2010 20:35:50 »
Neil,

Have you considered using the stick as a humane weedkiller?

Weeds ?..I see no weeds..I luff all plants !

Hang on...ewe want me to humanely kill Little Weed from Bill & Ben ?

Nooooooooo !!!

#### Geezer

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##### If I Move A Stick A light Year Long Will Both Ends Move At The Same Time ?
« Reply #5 on: 20/06/2010 22:43:23 »
Neil,

Have you considered using the stick as a humane weedkiller?

Weeds ?..I see no weeds..I luff all plants !

Hang on...ewe want me to humanely kill Little Weed from Bill & Ben ?

Nooooooooo !!!

Good grief! Is she still going? Isn't about time she took a dose of Paraquat?

#### The Naked Scientists Forum

##### If I Move A Stick A light Year Long Will Both Ends Move At The Same Time ?
« Reply #5 on: 20/06/2010 22:43:23 »