Quizzes & Puzzles1 min ago
Energy
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If energy can neither be created or destroyed then the amount of energy in the universe must be constant?? It therefore follows that the billions of car,train and plane journeys taken over the years have used no energy??
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//How can you come up with a balancing act (energy conversion) when there is a whole area of unexplained science.//
Every observation of ordinary matter obeys the conservation of energy laws.
We don't really have much idea of the nature of Dark Matter or Dark Energy. We don't even know if it can be transformed into other forms of energy let alone whether it would obey the same law. The name Dark comes not only from it not giving out light but also from knowing nothing about it.
Dark matter has never been directly observed nor seen to interact with ordinary matter other than gravitationally. Its existence is purported from the observation of how ordinary matter moves. Similarly dark energy which is purported through the accelerating expansion of the universe.
The real cause of these effects might never be known or could turn out to be something entirely unexpected.
Every observation of ordinary matter obeys the conservation of energy laws.
We don't really have much idea of the nature of Dark Matter or Dark Energy. We don't even know if it can be transformed into other forms of energy let alone whether it would obey the same law. The name Dark comes not only from it not giving out light but also from knowing nothing about it.
Dark matter has never been directly observed nor seen to interact with ordinary matter other than gravitationally. Its existence is purported from the observation of how ordinary matter moves. Similarly dark energy which is purported through the accelerating expansion of the universe.
The real cause of these effects might never be known or could turn out to be something entirely unexpected.
In a sense, in that you can draw energy from somewhere else and, from the point of view of the open system, it would appear as if there is more energy than there was before. One way this could happen for the coach is when you filled up the tank with petrol, effectively adding chemical potential energy. Of course, since this came from a petrol station, that system has lost energy.
The point then is that, while the sum of the total energy in the Universe remains constant, whereabouts that energy is and what "form" it's in (chemical, kinetic, heat, electrical, etc) can be very different indeed and is constantly changing. Then "energy use" tends to mean use of a particular kind of energy (normally something like chemical or electrical) to drive some process you care about (such as staying alive, or moving a coach between two cities), and doesn't care about the fact that the energy so used doesn't actually disappear. It just stops being so useful.
The point then is that, while the sum of the total energy in the Universe remains constant, whereabouts that energy is and what "form" it's in (chemical, kinetic, heat, electrical, etc) can be very different indeed and is constantly changing. Then "energy use" tends to mean use of a particular kind of energy (normally something like chemical or electrical) to drive some process you care about (such as staying alive, or moving a coach between two cities), and doesn't care about the fact that the energy so used doesn't actually disappear. It just stops being so useful.
@jim ^^^
Indeed. Energy conversion from type to type ends up as heat. I've heard the phrase 'degenerates into heat' used; perhaps not the best descriptor as it has overtones of decay, which implies destruction and is thus misleading.
The earth is a 'lossy' system and is dumping radiant heat into space all the time (give or take some greenhouse-effect bounce-back (or absorption/re-emission)).
@beso
Me:
////In nuclear fusion, such as inside the sun, energy is released (ie sunshine) but, as Einstein's e=mc^2 demands, there is a concomitant loss of mass. ////
//BTW. Many people assume that Einstein's famous law only applies to nuclear reactions.
In fact it is true of all reactions. The total mass of the products of an exothermic chemical reaction is slightly less than the reagents according to the same law.
11:48 Wed 08th Jul 2015
//
Really?
My understanding was that exothermic reactions are only able to release heat by virtue of the fact that the reactions involved in fabricating the energy-rich molecules, in the first place, were endothermic.
Photosynthesis temporarily violates "entropy is always increasing" by capturing energy from photons and using it to construct complex carbohydrates, which get modified into amino acids, polymerised into proteins, occasionally fossilised and baked until they break down into petrochemicals, which go on to last for 300-odd million years.
The stored energy is bond energy. No nuclei are fused or fissile. I am sure volumetric analysis of combustion products (light, sound, heat and mechanical work) versus fuel input would show no trace of mass loss, per Einstein.
Indeed. Energy conversion from type to type ends up as heat. I've heard the phrase 'degenerates into heat' used; perhaps not the best descriptor as it has overtones of decay, which implies destruction and is thus misleading.
The earth is a 'lossy' system and is dumping radiant heat into space all the time (give or take some greenhouse-effect bounce-back (or absorption/re-emission)).
@beso
Me:
////In nuclear fusion, such as inside the sun, energy is released (ie sunshine) but, as Einstein's e=mc^2 demands, there is a concomitant loss of mass. ////
//BTW. Many people assume that Einstein's famous law only applies to nuclear reactions.
In fact it is true of all reactions. The total mass of the products of an exothermic chemical reaction is slightly less than the reagents according to the same law.
11:48 Wed 08th Jul 2015
//
Really?
My understanding was that exothermic reactions are only able to release heat by virtue of the fact that the reactions involved in fabricating the energy-rich molecules, in the first place, were endothermic.
Photosynthesis temporarily violates "entropy is always increasing" by capturing energy from photons and using it to construct complex carbohydrates, which get modified into amino acids, polymerised into proteins, occasionally fossilised and baked until they break down into petrochemicals, which go on to last for 300-odd million years.
The stored energy is bond energy. No nuclei are fused or fissile. I am sure volumetric analysis of combustion products (light, sound, heat and mechanical work) versus fuel input would show no trace of mass loss, per Einstein.
Neither mass nor energy are individually conserved in exchanges of potential and kinetic energy. . . they are equivalent and related in proportion to E=mc^2.
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// I am sure volumetric analysis of combustion products (light, sound, heat and mechanical work) versus fuel input would show no trace of mass loss, per Einstein. //
By reaction products I was referring to the matter. The total mass of this matter after the reaction is less than the mass of the matter before the reaction by the exothermic energy according to E=mc^2
The point I was making is that the "missing mass" isn't just about nuclear reactions which are typically given as examples of the law.
By reaction products I was referring to the matter. The total mass of this matter after the reaction is less than the mass of the matter before the reaction by the exothermic energy according to E=mc^2
The point I was making is that the "missing mass" isn't just about nuclear reactions which are typically given as examples of the law.
//Neither mass nor energy are individually conserved in exchanges of potential and kinetic energy. . . they are equivalent and related in proportion to E=mc^2//
It is late but am I correct that the formula refers to the rest mass? And for moving objects we can add the kinetic energy which uses the Relativistic mass which can be substantially higher at high velocity.
My favourite case is the LHC where (if I recall correctly) the equivalent of a teaspoon of hydrogen gas at standard temperature and pressure acquires the kinetic energy of a maglev train at over 220 km per hour.
It is late but am I correct that the formula refers to the rest mass? And for moving objects we can add the kinetic energy which uses the Relativistic mass which can be substantially higher at high velocity.
My favourite case is the LHC where (if I recall correctly) the equivalent of a teaspoon of hydrogen gas at standard temperature and pressure acquires the kinetic energy of a maglev train at over 220 km per hour.
From the wiki
"The more common association of mass–energy equivalence with nuclear processes derives from the fact that the large amounts of energy released in such reactions may exhibit enough mass that the mass loss (which is called the mass defect) may be measured, when the released energy (and its mass) have been removed from the system; while the energy released in chemical processes is smaller by roughly six orders of magnitude, and so the resulting mass defect is much more difficult to measure."
So we are quibbling over the seventh decimal place in terms of mass loss, in a chemical reaction, as opposed to a fission/fusion event.
:-P
"The more common association of mass–energy equivalence with nuclear processes derives from the fact that the large amounts of energy released in such reactions may exhibit enough mass that the mass loss (which is called the mass defect) may be measured, when the released energy (and its mass) have been removed from the system; while the energy released in chemical processes is smaller by roughly six orders of magnitude, and so the resulting mass defect is much more difficult to measure."
So we are quibbling over the seventh decimal place in terms of mass loss, in a chemical reaction, as opposed to a fission/fusion event.
:-P
"... am I correct that the formula refers to the rest mass?"
Hmm. I'd say sort of. There used to be a concept of something called "relativistic mass", which is the mass of an object moving at a speed that is fast enough for people to care about relativity. I'm not sure it's really seen that way nowadays, though. A matter of interpreting the same thing, anyway, in a different way.
The technically correct formula is E = y m c^2, where y is the Lorentz factor 1/Sqrt[1-v^2/c^2] for an object moving at speed v, and m is the mass (or "rest mass", if you prefer") of the object in question.
(The even more correct version is E^2 - p^2 c^2 = m^2 c^4, where p is the momentum of the moving thing, and now you can also adapt the formula for particles that have no mass -- eg photons.)
Hmm. I'd say sort of. There used to be a concept of something called "relativistic mass", which is the mass of an object moving at a speed that is fast enough for people to care about relativity. I'm not sure it's really seen that way nowadays, though. A matter of interpreting the same thing, anyway, in a different way.
The technically correct formula is E = y m c^2, where y is the Lorentz factor 1/Sqrt[1-v^2/c^2] for an object moving at speed v, and m is the mass (or "rest mass", if you prefer") of the object in question.
(The even more correct version is E^2 - p^2 c^2 = m^2 c^4, where p is the momentum of the moving thing, and now you can also adapt the formula for particles that have no mass -- eg photons.)
I've long understood that moving matter cannot be accelerated to, or beyond, light speed, due to the "mass-gain" problem. As mass tends to infinity, acceleration tends to zero, so it can only cruise along, a whisker short of light speed.
This thread is the first time it has been made clear to me that, while the relativistic particle gains mass, as it acquires the energy used to thrust it along, it merely 'bears' this energy: - no new matter is brought into being. Slightly dissapointed because there are exotic things in space which eject streams of energy at relativistic speeds but nothing can come from that except photons.
This thread is the first time it has been made clear to me that, while the relativistic particle gains mass, as it acquires the energy used to thrust it along, it merely 'bears' this energy: - no new matter is brought into being. Slightly dissapointed because there are exotic things in space which eject streams of energy at relativistic speeds but nothing can come from that except photons.
You do need to be careful with these things, though, Hypo. While it's true that the "infinite mass" picture is perhaps misleading, it's also true that particles travelling at a high speed can release that energy in the form of (usually) photons, and these photons can then be energetic enough themselves to turn into actual massive particles such as electron/ antielectron pairs. These can then decay further, etc etc, and at least for a short while some mass can be added to the Universe. But it can't last for long.
Basically you have to be careful once quantum effects get thrown into the mix. But in terms of the original particle, at least, its mass is usually seen as effectively constant, and it's the energy (and momentum) that changes and can grow towards infinity.
Basically you have to be careful once quantum effects get thrown into the mix. But in terms of the original particle, at least, its mass is usually seen as effectively constant, and it's the energy (and momentum) that changes and can grow towards infinity.
