Energy

[bill barlow]

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??

[fiction-factory]

http://www.scientificamerican.com/article/energy-can-neither-be-created-nor-destroyed/

[fiction-factory]

It's changed from one form to another

[Buenchico]

It depends upon what you mean by 'use'.

Vehicle engines simply convert chemical energy (or electrical energy) into kinetic energy and thermal energy. So, as you've suggested, the total amount of energy has remained unchanged. However specific types of energy have been 'used' (in the sense that they've been 'converted') during those processes.

[Buenchico]

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/energy/heatrev4.shtml

[bill barlow]

So are we saying driving a coach with 52 passengers from London to Glasgow does not use any energy??

[fiction-factory]

It uses petrol (or is it diesel for a coach)

[Buenchico]

The coach 'uses' chemical energy but converts that to kinetic energy (and also some unwanted thermal energy).

[bill barlow]

Thanks. Confusion seems to be over the definition of "uses" You have explained it converts the energy presumably with no energy loss?? So can we say no energy is consumed? or what is the word?

[mibn2cweus]

Perhaps the distinction of 'useful' energy is a consideration here. It would be very difficult and costly if not impossible to return the energy converted for transportation back into . . . petrol?

[sandyRoe]

Didn't Swift write of converting cucumbers into sunshine?

[Buenchico]

He did, indeed, Sandy:
https://ebooks.adelaide.edu.au/s/swift/jonathan/s97g/chapter21.html

However such a process would break the Second Law of Thermodynamics which (as someone who has taught Physics) I ought to fully understand but I have to admit that I don't ;-)

[sandyRoe]

Glancing through that^ I see mention of an even more unlikely project than the cucumber one, trying to convert excrement back to its original food.

[Buenchico]

^^^You've obviously never eaten in McDonalds, Sandy ;-)

[Hypognosis]

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. It is tiny, compared to the mass of a proton, but, if you add up the masses of the nucleii which go into the fusion and compare with the mass of the fusion product, there is that discrepancy.

The sun is therefore trading mass for electromagnetic emissions (of which heat and light are just two narrow slices).

Multiply up by the billions of suns and thousands of billions of galaxies and the universe is, likewise, losing mass and turning it into electromagnetic radiation.

No wonder expansion is accelerating!

[Old_Geezer]

You have hit the nail on the head regarding your problem. It is how you are using the word "use".

One uses energy in that you used it to convert it from one form to another and used the resulting reactions to allow you to achieve something you wanted. You didn't use it in the meaning that it is no more. It still exists. It is no more in a useful form, but it's still around somewhere.

I suggest looking at a thesaurus to see if there are better alternative words for each of those uses of the word "use".

Perhaps it is clearer to say you used the effects of energy conversion rather than the energy itself ?

[jim360]

The other thing you have to remember when interpreting the statement "energy can neither be created or destroyed" is that it only applies to a "closed system". A closed system is something in which the total energy remains constant no matter what physical process happens (so that's a bit of a circular definition, but can't be helped). A coach travelling from London to Glasgow is not a closed system, and so it will have used up energy up along its journey. Only when you include the surroundings -- road and atmosphere, mainly -- will you find that the total energy remains constant, for example as heat that's been transferred from the coach.

[beso]

//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.

[Zacs-Master]

So,where does this leave us all with Dark Matter?

[jim360]

Not sure what you mean ZM. Dark Matter will be bound by the same thermodynamics as everything else. Perhaps you mean Dark Energy?

[Zacs-Master]

i may have meant dark energy but on the OH I might have meant:
How can you come up with a balancing act (energy conversion) when there is a whole area of unexplained science.