A system possesses energy if it has the ability to do work.
Work shifts energy from one system to another.
Energy is …
Energy can exist in many different forms. All forms of energy are either kinetic or potential. The energy associated with motion is called kinetic energy. The energy associated with position is called potential energy. Potential energy is not "stored energy". Energy can be stored in motion just as well as it can be stored in position. Is kinetic energy "used up energy"?
|type||motion||examples and subtypes|
|motion of macroscopic objects||machines, muscles, projectiles, wind, flowing water, ocean waves, sound, …|
|random motion of microscopic particles of matter (molecules, atoms, ions)||heat, fire, geothermal, …|
|bulk flow of charges (electrons, protons, ions)||household current, AC and DC circuits, lightning,…|
|disturbance propagating through electric and magnetic fields (classical physics) or the motion of photons (modern physics)||radio waves, microwaves, infrared, light, ultraviolet, x‑rays, gamma rays|
|force field||quantity in field||examples and subtypes|
|gravitational||mass||roller coaster, waterwheel, hydroelectric reservoir, …|
|electromagnetic||charge||electric, magnetic, chemical, elastic, …|
|strong nuclear||color charge||nuclear reactors, nuclear weapons, …|
|weak nuclear||lepton number||radioactive decay, …|
For those who want some proof that physicists are human, the proof is is the idiocy of all the different units which they use for measuring energy.
|unit||joule equivalent||other equivalent||reference|
|watt hour||3.6||kJ||3600 W s||"|
|kilowatt hour||3.6||MJ||1000 W h||"|
|thermochemical calorie||4.184||J||(by definition)||heat|
|International Table calorie||4.1868||J||(by definition)||"|
|International Table Btu**||1.05505585262||kJ||(by definition)||"|
|cubic meter natural gas||37–39||MJ||(variable)||chemical|
|ton of oil equivalent||41–45||GJ||(variable)||"|
|ton of coal equivalent||29.3||GJ||(approximate)||"|
|ton of TNT||4.184||GJ||(by definition)||"|
|*||The kilocalorie is also known as the kilogram calorie, dietetic calorie, food calorie, and Calorie (with an uppercase "C").|
|**||Btu is the abbreviation for "British thermal unit".|
|***||Quad is the shortened form of "quadrillion Btu".|
|atomic mass unit||u||muc2||= 1.492 × 10−10 J|
|electron volt||eV||e||= 1.602 × 10−19 J|
|hartree||Eh||2R∞hc||= 4.35974381 × 10−18 J (exact)|
|inverse meter||m−1||hc||= 1.986 × 10−25 J|
|inverse second||s−1||h||= 6.626 × 10−34 J|
|kelvin||K||k||= 1.381 × 10−23 J|
|kilogram||kg||c2||= 89,875,517,873,681,764 J (exact)|
|c =||speed of light in a vacuum||k =||Boltzmann constant|
|e =||elementary charge||mu =||atomic mass unit|
|h =||Planck constant||R∞ =||Rydberg constant|
Τοῖς μὲν οὖν λέγουσι τὴν ἀρετὴν ἢ ἀρετήν τινα συνῳδός ἐστιν ὁ λόγος· ταύτης γάρ ἐστιν ἡ κατ᾽ αὐτὴν ἐνέργεια. διαφέρει δὲ ἴσως οὐ μικρὸν ἐν κτήσει ἢ χρήσει τὸ ἄριστον ὑπολαμβάνειν, καὶ ἐν ἕξει ἢ ἐνεργείᾳ. τὴν μὲν γὰρ ἕξιν ἐνδέχεται μηδὲν ἀγαθὸν ἀποτελεῖν ὑπάρχουσαν, οἷον τῷ καθεύδοντι ἢ καὶ ἄλλως πως ἐξηργηκότι, τὴν δ᾽ ἐνέργειαν οὐχ οἷόν τε· πράξει γὰρ ἐξ ἀνάγκης, καὶ εὖ πράξει. ὥσπερ δ᾽ Ὀλυμπίασιν οὐχ οἱ κάλλιστοι καὶ ἰσχυρότατοι στεφανοῦνται ἀλλ᾽ οἱ ἀγωνιζόμενοι (τούτων γάρ τινες νικῶσιν), οὕτω καὶ τῶν ἐν τῷ βίῳ καλῶν κἀγαθῶν οἱ πράττοντες ὀρθῶς ἐπήβολοι γίνονται. With those who identify happiness with virtue or some one virtue our account is in harmony; for to virtue belongs virtuous activity. But it makes, perhaps, no small difference whether we place the chief good in possession or in use, in state of mind or in activity. For the state of mind may exist without producing any good result, as in a man who is asleep or in some other way quite inactive, but the activity cannot; for one who has the activity will of necessity be acting, and acting well. And as in the Olympic Games it is not the most beautiful and the strongest that are crowned but those who compete (for it is some of these that are victorious), so those who act win, and rightly win, the noble and good things in life. Ἀριστοτέλους Aristotle
Actual, or Sensible Energy, is a measurable, transmissible, and transformable condition, whose presence causes a substance to tend to change its state in one or more respects. By the occurrence of such changes, actual energy disappears, and is replaced by Potential or Latent Energy; which is measured by the product of a change of state into the resistance against which that change is made. (The vis viva of matter in motion, thermometric heat, radiant heat, light, chemical action, and electric currents, are forms of actual energy; amongst those of potential energy are the mechanical powers of gravitation, elasticity, chemical affinity, statical electricity, and magnetism.) The law of the Conservation of Energy is already known, viz.:—that the sum of all the energies of the universe, actual and potential, is unchangeable. The object of the present paper is to investigate the law according to which all transformations of energy, between the actual and potential forms, take place.