Not always easy to understand either, it relates always to the surrounding space. For example, the unevenness of a dam gets an energy due to the difference in level : it is the energy given by gravity : the same mass of water supposed without any difference of level does not give any energy. The nature provides numerous examples and first of all, the sun which heats ourselves with its fusion energy (that we are unable to reproduce for we make only atomic fission), sea waves, tide, winds, storms, water falls, volcanoes, tectonic plates, but also radiation and the last but not the least, fire, always in veil, for it leads to a inferior level of energy, which is not easy to catch, excepted examples of an object which rolls or falls or a spring that release, a liquid that spills, so all which give us some torments..

A large black cloud (cumulus), with a large base flat and low, conceals a fantastic energy, we could compare at a small atomic bomb ; that is to say 1 Megaton (million ton of an explosive). It is traversed by ascending and downward currents of 300, 400 km an hour established on a large surface. Such clouds are forbidden for planes to go through and they must imperatively deviate. But to collect this energy, where must the wind mill to be fixed ?

Despite of their speed referring to the ground, two satellites side by side do not have any energy between them, but they have some compared to the ground and one notices it when some pieces fall. On the other hand, if it is wanted that a satellite approaches the other, he will be necessary to give it a small blow of engine, i.e. energy, but by doing this, gaining in energy, the rocket rises in altitude !! is this unresolved ?

On the level of the electron in an atom, it is similar : an electron which receives energy passes on a higher level and an electron which loses some " goes down " while yielding an energy which will generally appear in the form of radiation, such as the light. And if one makes fall together a great number of electrons, one makes the laser light! ! (which does not exist in nature).


Energy can be given also by the heat (fire, vapour engines, atomic power plant (*), action (battery, powder/ gas explosion).
(*) the atomic reaction of uranium produces heat which runs turbines then electricity generators like the coal does (we are not able to turn directly atomic power into electricity). The first effect of an atomic bomb is the very high heat that melt everything and produce a big blow near the explosion spot. Radiation damages follow. (*) In the USA, not far from Washington, a former coal mine is burning for nearly 50 years, after an accident. Attempts to extinguish the subfire have all failed and they had to evacuate the nearby community ; a road access is banned, the soil and tar are cracked and one child failed to be engulfed in a sudden flaw. Smoke and dangerous gases are permanently escaping from the soil.

Relation between measuring units of energy There are various units to measure an energy, in general adapted to the field concerned (work, heat, electricity.): the horse vapor, used for long, the Joule, the small calorie and the big one (kilogram calorie), the kilowatt-hour.. There are relations between them, such as this one, below (energy value of food, which is a calorific unit). here 257 kcal (kilogram calorie = 1000 calories) = 1076 kJ (kilojoules).

Kinetic energy: You can have big damages at low speed if the mass is important because the energy is high or with a small mass and a great speed ; the speed count for the square digit in the formula but an insect can fall in any risk. Cosmic or X-rays are very energetic due to their very high speed. The TGV has more energy than a normal train, even with less mass (weight), because energy is increasing with the square speed digit.

A car running has energy but a parked has not energy ; therefore, the parked car has energy because the earth rotate but we can used it because we rotate with it ! we need a fix point outside the earth to catch it.

CARS !! The worst example of energy, after weapons, is given by cars on a free way ; close to another, you don't perceive the danger because the speed is nearly the same. And at 80 mph, the energy of the vehicle and yourself are very high and you are in great danger, for example if the other car cut your lane or breaks suddenly. If you stand still on the side of a free way, watching at the cars, you feel reality of energy and it is actually very very frightening to see these projectiles ; and it is worst at night. More than the speed itself, think to the distances between the others, it is the only salvation.

It comes from the lightning, the static electricity (see above) or better for our comfort, from a generator (pile, the invented first, battery, magneto, dynamo); one naturally establishes an equivalence between the mechanical or chemical energy and the electric power which result from it. The current unit is the kilowatt-hour (1000 Watts during one hour) which corresponds to a generator (source of energy) which would deliver a current of 10 amps (intensity of the current) during one hour with a tension of 100 volts (tension of the current). One summarizes that by the formula
W = U (volts) * I (amps) * T (time) (the signs * means "to multiply" although it is commonly a simple dot).
To understand these terms and the formula, imagine that the current (I amps) is a flow, like that of a tap, more or less significant and that the tension (V volts) is the pressure of water on the outlet side of the tap. The power is P (Watts) = U * I.

Practical application; flashlight lamp.
Note : With the LED, the light bulb time seems to be over ! it's only a drastic lower consumption, nearly the tenth. I can affirm that THE LED WILL LARGELY INCREASE THE ELECTRICITY CONSUPTION instead of lower it due to their proliferation. Calculations that follow are always right, although with big consumption values for a single lamp.

 A flashlight functions with two cells of 1,5 volts, one put one behind the other in the lamp. It is said that they are connected in series, as the whole deliver 3 volts. The bulb indicates 2,5 volts and 0,3 amps. Such conditions give a power of P = U * I, that is to say 0,75 Watts. It is nearly reality because the tension on the outlet side of the two cells will drop  rather quickly under 3 volts (there are losses in the cells (which heat a little) because of their internal resistance. If you light during 15 mn, you will have spent 0,75 * 0,25 (1/4 of hour) = 0,1875 kilow/h. One cannot know how long that will last because the manufacturers are dumb on the capacity (energy) their cells.
However, I drove some tests myself that give an idea, but it is in French ! see and translate "cells and batteries"
Advice : best is to note prices and duration of the cells to compare them. The good bargains are often for the salesman. Flashlight ; check the bulb of your lamp. For a lamp with two cells (3 volts), you may find it beneficial to put a bulb of 2,5 volts - 0,3 amps or 2,2/2,3 volts - 0,3 amps at magnifying glass (the bulb comprises a round nose). It is with these that the result is often the best. That also depends on the reflectors, therefore test them. One now finds bulbs supposed being more powerful (halogens) but beware, they consumes enormously and reads 1,3 amps !! Replace the bulb by one 2,5 (volts) - 0,3 A (amps) or one 2,2/2,3 v - 0,3 A with magnifying glass; you will see better and much longer.

The manufacturers of electrical appliances are very often linked with the manufacturers of cells, which wield more than the apparatus itself ! Radio set ; alas, if the radio set consumes, one can limit the loss : if you have an adjustment of bass, super bass (méga bass), regulate at low or cut because bass consume much more energy than the high tones, especially at high level sound power. For a regular broadcasting, speaking or so, lower also the volume, by preserving a pleasant listening, because the power consumption depends much on it.

To anticipate a possible shortage of energy (oil, gas, uranium ..) or ensure independence, all imaginable forms of energy are being tested, and the imagination is totally freed in this area, after the yet tested waves, tides, wind turbines, photovoltaic cells, coal gasification by semi combustion without extracting it (*) or recovery by inertia during each braking (cars, buses, trains..).
There are more surprising, like in a station of Japan, where they are attempting to get a current by the people walking on piezoelectric elements!  More promising is the osmotic pressure exerted between two water tanks, one containing pure water and other salted water, separated by a porous membrane that let the water pass through but not the salt. Nature is strange and pure water tends to move in the other tank to reduce its salinity : a high pressure is created, then a spray of salt water which runs a turbine.

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Electrical power, vacuum power : a vacuum cleaner of 1500 Watts has a power of aspiration of 30 kPa: 30 kPa means 30 kilo-Pa either 30.000 Pascals, equalizes about to 30.000 divided by 9,81 = 3050 kg per square meter, or 305 grams per square centimetre, or still the equivalent of a water column of 3,05 meters or 3 divided per 13.6 (density of mercury) = 225 millimetres (mm) of mercury (Hg) or also 300 millibars (that's all !! ). It is this aspiration (depression) that it is necessary to compare. To finish, that returns to almost 1/3 of the atmospheric pressure, which is worth in general on the sea level 760 mm of mercury or 1013 millibars (thousandth of bar). With all these equivalences, no manufacturer can more mislead you.