# What is energy really? [duplicate]

When we talk of momentum , we can say that momentum is a measure of amount of motion contained in the body but I cannot get a similar intuition for energy energy is a measure of what? Or is it just a certain mathematical quantity that just remains conserved and is thus used for solving problems etc. And I don't seem to be satisfied with statements like 'energy is capacity to do work' because then again I ask what is work then...it's just not very clear I'm unable to get a hold of the concept..not even sure of what exactly I am confused about..maybe a historical significance of the concept of energy and the progresses made to define it might help,requesting suitable directions.

• This is a very deep question with no clear single "sound bite" kind of answer. The concept of energy is pretty fundamental to physics and is tied, via Noether's theorem, to the concept of time-translation symmetry. At an intro to physics level, Energy is simply "the ability to do work". – enumaris Aug 29 '18 at 21:00
• Possible duplicates: physics.stackexchange.com/q/3014/2451 and links therein. – Qmechanic Aug 29 '18 at 21:19

On an elementary level, you can think of energy like money in a bank account. Spending money is like performing work and saving money is like storing up work.

If you dump a large amount of money out of your account in a short time, you are exerting lots of influence, which is like saying that the rate of performing work is equal to power.

If you have lots of money saved up in your account, you can think of it as if it were "stored work" which you can tap into in the future.

And when you are broke, you have no ability to exert influence, which is like saying that without energy on hand, you cannot perform work.

• If only bank account zeroes were as arbitrary as the zeroes of energy... – enumaris Aug 29 '18 at 21:19
• there are, of course, limits to the analogy... – niels nielsen Aug 29 '18 at 21:27

When you think of energy you can think about an internal powerful resource that a body has. More amount of this resource means that the body can reach more velocity $E = \frac{1}{2}\cdot m \cdot v^2$ in some way. Or he can otherwise transfer this resource through thermic activity, for example if it gives it it becomes colder and slower (looses velocity), gaining it it becomes hotter and faster (gains velocity). It can also gain this resource if the energy is potential, for example being in a high place on earth, falling, it will gain velocity. Maybe think about energy as resource that can be consumed to make the body move faster, gain velocity.

This is not a scientific answer but a general-intuition one.