Does a compressed spring weigh more than an uncompressed spring? The answer is surprisingly yes!
To understand why this is the case, we only need to look at the famous equation, e=mc². Since energy is directly related to mass, adding energy to a system affects the mass the following way: m=e/c². So if we were were to add 1,000 joules of potential energy to a spring, its mass would increase by 1,000 / c² or 1.113 × 10^-14 grams.
The same principle can be applied any time we add energy to a system. For example, heating an object increases its mass, and accelerating an object increases its mass as well. In fact, the reason why it is impossible to go the speed of light is because as an object approaches the speed of light, its mass increases so much that the engines require more and more energy to increase its speed. Accelerating to the speed of light would take an infinite amount of energy.
While these concepts go against common sense, the mathematics behind them are sound.
Sunday, August 16, 2009
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Of course the weight is negligible at such a small change. I thought, physics not being a strong suit for me, that the energy in a spring is the same whether compressed or not. Or does that have to do with potential energy?
ReplyDeletethere are different types of potential energy. in this case we would be giving elastic potential energy by compressing it.
DeleteBah, I am an idiot, I remember the answer to this now. The energy is added from the force of compressing the spring.
ReplyDeleteno it's not. this is completely wrong.
Deleteum.... He's actually right.
DeleteYou aren't an idiot, it took humans a long time to learn this.
ReplyDeletehumans never learned this. this is wrong.
DeleteIn equation e=mc^2, the mass is relative.so how it is possible for rest mass. Also the theory of relativity is the theory of moving objects.
ReplyDeleteer..no.. actually that e=mc^2 is ONLY for resting objects, moving objects are E = root ((m_0*c^2))^2+(pc)^2)
Deletewhere m_0 is the resting mass and PC are the euclidian momentum vectors (0 if at rest, which results in E=mc^2).
The full energy of an object is only applicable at speed tho, an object standing still has an "energy level" that, however, does nothing if the outside parameters do not change. If you change the compression of the coil you add to that energy level by giving it eleastic energy (this energy can dissipate by plastic change of the coil to a more dense form)and add some (neglegibly small) amount of mass.
Thanks for sharing this useful information! Hope that you will continue with the kind of stuff you are doing.
ReplyDeleteCompression springs
This is nonsense. The energy is not converted into mass, hence a compressed spring doesn't weigh more at all... unless you're going to contend we can remove the spring and be left with the extra mass that materialized due to the added energy.
ReplyDeleteRight? Your argument makes sense to me... Because if you lifted the mass higher, adding potential energy in the form of height (mgh), would that also cause the spring to increase in mass? In that sense, it's "mass" would be relative to it's proximity to other objects?
DeleteI looked into it and the way I understand it, the claim is right but not in the way the article implies. Not ALL of the energy you put into a spring gets converted into mass. If that was the case, there would be no energy left to actually compress the sting. However, during compression some elementary particles of the Sping's atoms will be elevated into a higher energy state e.g. they get accelerated. As those particles approach the speed of light, they gain a slight mass increase due to the relativistic conservation of momentum. The effect is very tiny an absolutely negligible in any practical sense.
Deletehttp://galileoandeinstein.physics.virginia.edu/lectures/mass_increase.html
Einstein would beg to disagree: http://en.wikipedia.org/wiki/Mass_energy_equivalence
Deletealso, in order to have a mass change of 1 milligram, 0.001g, you would need to add 90 Terajoules of energy, compared to the 63 TJ of the Hiroshima Atomic Bomb.
So even if the physics were right (which it is not), you would need an absurdly large amount of energy to try to see any increase at all.
To be clear, @alcalde, I completely agree. The "debunker" is full of bunk.
Deleteno, alcalde is wrong. Energy and mass have a direct and complete correlation according to most physicists theories. That means energy IS mass and mass IS energy.
DeleteThis is hard to understand I know but thinking there is "conversion" going on here is wrong, there is no converting anything to anything, they are both one and the same, it's useless to disconnect the two and see where they're needed.
And yes, the change in mass is ridiculously small, so what? The saying "does it weigh more" never mentioned a scale. We can assume that these theories are largely correct since all observations till now fit.
About the energy levels, you are thinking very, very small. These calculations also work on other planets, galaxies and so on, potential, kinetic and rest energy change masses of suns, planets, galaxies and so on. Again, the "myth" was only "changes weight", no scale.
@Aaron Wilson, yes the mass changes, however the further you get from the center of the gravitational object, the smaller your gravitational constant g becomes (g=g_0*(r/r+h)^2, where r is the mean radius, h is height above sea level and g_0 is the gravitational constant) so potential energy E=mgh would constantly become smaller the higher you go, this results in an energy flux and thus a mass flux.
This "debunking" is COMPLETELY INCORRECT. Matter can only ever change into energy in an atomic reaction. And ENERGY CAN NEVER CHANGE INTO MATTER. I suggest you read your physics before you try to "debunk" any further physics related questions.
ReplyDeletehttp://en.wikipedia.org/wiki/Mass_energy_equivalence
But your link includes this:
Delete"A spring's mass increases whenever it is put into compression or tension. Its added mass arises from the added potential energy stored within it, which is bound in the stretched chemical (electron) bonds linking the atoms within the spring."
http://en.wikipedia.org/wiki/Mass_energy_equivalence#Practical_examples
[citation needed]
DeleteExcept that "citation needed" is an understatement in this case.
Extraordinary claims require extraordinary evidence. This sounds like someone took E=MC^2 a bit too literally.
Citation found:
Deletehttp://books.google.com/books?id=tpU18JqcSNkC&lpg=PP1&pg=PA87#v=onepage&q&f=false
That blew my mind. But it does seem to have a nice symmetry with the mass increase that accompanies kinetic energy (e.g. as an object's speed approaches that of light, the objects mass approaches infinite).
Have a look at this:
Deletehttp://en.wikipedia.org/wiki/Talk:Mass%E2%80%93energy_equivalence#Okay.2C_and_let.27s_point_out_early_that_mass_is_never_converted_to_energy.2C_and_vice_versa
If the mass/energy of a given system is increased by mechanical tension, that increased mass/energy must come from somewhere. It cannot be created out of thin air. Therefore, the compression mechanism and/or the surrounding air would have to loose mass/energy in order to effect an increase in the spring being compressed.
ReplyDeleteAs a system, the mass/energy of the spring, the compression mechanism, and the surrounding air would remain constant.
The problem with this thought experiment (and let's be clear this is only a thought experiment - no empirical data is available here) is that it is impossible to have the spring compressed and also weigh only the spring or only the compression mechanism. They can only be measured as a system or individually without the compression. Therefore, once they become a system, the weight of that system does not change if one part of the system compresses another.
so, if I have a spring and a rope on a very precise scale and the weigh X. If I tie the rope around the spring to compress it and weight them again, they will weigh X+Y, where Y > 0?
ReplyDeleteFrom my gut understanding no, as the energy added in compression is taken from the atomic bonds within the rope, thus negating the change in energy ergo mass.
DeleteThe confusion here is caused by a misunderstanding of terms. When a system composed of an uncompressed spring is compressed, it has energy/relativistic mass added to it. Relativistic mass and energy are equivalent. However "weight" refers only to gravity's relationship with REST mass, not relativistic mass. Energy cannot become rest mass, therefore the compressed spring will not weigh more.
ReplyDeleteWhen a spring is compressed, it DOES gain relativistic mass. However, since energy and relativistic mass are equivalent, this is the same as saying "When energy is added to a system, it has more energy."
So, if I got this right a TV thats on has more relativistic mass, then when its off?
DeleteI believe that is correct. ANYTHING added to a system, energy or matter, increases its relativistic mass. A tv that is on has more Rel. Mass than one that is off. Heat that tv up in an oven and you have added even more Rel. Mass. Fire it out of a cannon and you've got still more.
ReplyDeleteNow as has been correctly pointed out by other posters, the proportion of the total Rel. Mass represented by the electricity, by the heat, by the motion, by the compression, is extremely miniscule having to be expressed in scientific notation. In order to double the Rel. Mass of our TV, we would have to accelerate it to about 86% the speed of light, which would require a staggering quantity of energy.
Anyway, I am not an expert, just a hobbyist, so I welcome correction. But I think it starts making more sense when you learn to think about Matter and Energy as just different forms of the same kind of "stuff", as counterintuitive as that feels.
Not only is it true but the compressed spring is warmer also.
ReplyDeleteA spring made of iron will weigh more than one made of plastic (slinky, etc.) The same exact principle applies here.
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