Will it take years for the “movement” to be felt from the other end?
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A mechanical impulse will travel through the material at the material’s speed of sound.
For steel this is about 5100m/s, so the end will move in 58,782 years.
The speed of a mechanical pressure wave in a solid object is the speed of “sound” in that object. It is much much much less than the speed of light. So it would take many years indeed before the other end reacts to the pressure of the push.
The motion of the everything moves via a vibration wave… think of a spring on a microscopic level. If the rod is hardened steel, the speed of sound is 3150 m/s. On light year is 9.46×10^15 meters. Assuming the rod didn’t just absorb that vibration and convert the energy to heat, it would take about 95,000 years for the other end to feel it.
https://www.rshydro.co.uk/sound-speeds/
There is no such thing as a solid rod. Everything acts like a spring at some level. So when you push on the end of the rod it will compress and it takes some amount of time for this pressure to move along the rod. The movement is the same as sound which means that the movement goes at the speed of sound through the material. For steel the speed of sound is about 3-5km/s. About 10-20 times faster then the speed of sound in air. But still orders of magnitude slower then the speed of light. So even at the fastest end of the spectrum it would take about 60.000 years for the movement to go through the entire light year long rod.
It would probably take decades. Kinetic energy moves through a substance at that substance’s speed of sound. Kind of like how sound travels faster through water than air. Even in an incredibly hard substance like diamond the speed of sound is only 12000 m/s. That’s 5 digits to light’s 9.
Speed of sound through the material x distance. Pushing the rod will compress it, the speed that compression wave will move through the rod is the the speed of sound.
Check https://www.engineeringtoolbox.com/amp/sound-speed-solids-d_713.html for the speed in various solids
it’s not a rod if it’s that long in one direction vs thickness
so it’ll be like pushing a very thin hair strand
meaning nothing happens on the other side
Given the respective mass, the effect on the rod would be negligible. You’d just push yourself away from it.
Depends on the material.
If you have something squishy like rubber, more energy will go into compressing it than moving it.
Can someone confirm or disprove my theory? If you had some perfectly rigid material that couldn’t squish under pressure (and would instead shatter) then it would go instantly? Or at the speed of light?
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