this is regrading law of conservation of energy?

Question

A coal piece when heated on ground it gives some heat energy .
When it is taken to a certain height its potential energy increases.
When it is heated at this position it should give more heat acc. to L.O.C .But it gives the same amt of heat energy as it gave on the ground.Where does this P.E go ?

Answer 1

That is not a correct understanding of the law of conservation of energy.

The coal piece has a certain amount of potential energy because of its chemical state. This potential energy is released as heat when its chemical state is changed by burning in oxygen.

The potential energy gained by that piece of coal when it is lifted to a height is provided by the work done by an external agency in lifting that piece of coal to that height from ground level. So, that potential energy is again recovered as kinetic energy if the piece of coal is dropped from that height.

Potential energies are of various types and one cannot be converted into another. Corresponding to each type of energy (motion due to gravitation, motion due to spring, heat due to chemical reaction etc.), there is a potential energy.

Energy is always being converted from one form to another form and is conserved in these transformations in a closed system (that is the universe). And law of conservation of mass and energy is the correct law to be applied.

Answer 2

The gravitational potential energy and chemical potential energy are separate here. If you were to burn the coal high-up in a completely sealed container, then you would have resultant ash,smoke and gasses produced with the same weight as the initial lump of coal. The gravitational potential energy hasn't "gone" anywhere. It is only the chemical potential energy which has been converted into heat.

There are essentially only two types of energy: potential and kinetic. Heat energy is just the cumulative kinetic energies of the atoms, the hotter things get, the faster the constituent atoms move about, and the more heat energy is present. Potential energy is just stored energy which hasn't been converted into kinetic energy.

All energies can be converted from one into the other. For example chemical potential energy in the coal can be converted into first kinetic, then gravitational energy by driving a steam train up a hill. Gravitational potential energy can be converted into kinetic energy by dropping it, when it hits the ground the kinetic energy is converted into heat energy by friction, which heats the coal up slightly.

Answer 3

Where from, do you expect it to come ? What we know about energy is, 'it exists around us' There is always some change in the forms of energy. The total remains the same. When two persons are having a total of 100 dollars, what ever the way they share these amounts, the total will remain as 100 dollars. This is law of conservation of energy . Your question is how did they get 100 dollars. The law cannot answer this question. It is a statement about sharing the money and not the source of income for the two. As long as they do not interact with others the 100 dollars will not change. They cannot create dollars or loose dollars as long as they are there together. Now if another person joins with these two with another 50 dollars, then the total will now become 150 dollars and the law is now about the total of 150 dollars and not about 100 dollars. The law do not question how did the third person get 50 dollars. If you include all world and all nations the total amount of money will remain the same. If you include persons who have gone to mars or other planets, again the total amount will remain the same.

Answer 4

The potential energy went up in smoke. You didn't defy the laws of nature. You hid the evidence when you turned a nice respectable lump of coal into a totally uncivilized bunch of gasses and smoke particles that are impossible to keep track of. When the things that were once coal return to the ground they will lose the potential energy that was used to raise them up, but they will probably be scattered around the globe by then, except for the poor little cinder left behind.

Answer 5

Potential energy (in mechanics, not thermodynamics) is called potential because it can potentially be converted into kinetic energy.(energy of motion)

This happens when the body is dropped.

Now, when the body hits the ground there is a release of heat energy if the impact is inelastic. But the conversion here is from kinetic energy into heat.

Answer 6

The potential energy is not converted to heat. Consider that if there were so, you could take it back down to the bottom of the coal mine, burn it and generate cold. Potential energy due to vertical elevation does not convert to heat chemically.