ergs joules kilocalorie
foot-poundals foot-pounds kg force-meter
BTU kilowatt-hour horsepower-hour

Energy megaConverter #7

Introduction and Overview
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Energy is the work done within a system. Or the potential for such work. Work is defined as applying a force through a certain distance. The formula for energy is force x distance, or in the case of kinetic energy, mass x velocity squared. (Note that both formulas share the same set of basic units) Thus, energy can be represented by any force unit times any length unit, but few but the common ones would have any practical application.

Energy is a quantity that can be neither formed nor destroyed, only changed from one form to another.

There are three basic forms of energy: kinetic, potential, and thermal. Kinetic energy is the energy of motion. If you don’t think there is energy in motion think of a car hitting a tree. The kinetic energy of a moving object is represented by MV squared. Potential energy represents forms such as chemical, atomic, gravitational, material stress, etc. A boulder on a mountaintop has potential energy because if it falls off, it will accelerate and gain more and more kinetic energy, until it hits the bottom where the kinetic energy is transformed into heat energy. The boulder falling is equivalent to work because the gravity that causes the boulder to fall is a force and it falls through a given distance. Gasoline has potential energy because it will burn and creates heat which can then be transformed into kinetic energy which can be used to do work. Atoms have potential energy because they can be fissioned or fused in nuclear reactors to produce heat which turns a steam turbine which does work.

Energy was not a quantity people dealt with in earlier times, and so the British and metric units are the only ones in common use. This megaConverter converts between the most commonly used energy units of today.

For a more comprehensive treatment of measurements, find "NTC’s Encyclopedia of International Weights & Measures" by William D. Johnstone at your local library. For a better discussion of energy, see any college physics textbook.

* Much of our written history still refers to things in common units. The Bible does not refer to meters or kilograms, but to cubits and stadia, or shekels and drachma. Wouldn't it be nice to know what they were talking about way back then? Now you can use megaConverter! For a more complete listing of ancient, foreign, and obsolete measures, download our 'megaSpreadsheet' of conversions in MS Excel format.

Glossary of Conversions:

erg, joule, foot-poundal, foot-pound,
kilogram force-meter
These are all direct units of work. A force times a distance. The erg is the name for the dyne-centimeter. The joule is the name for a newton-meter.

A calorie is the amount of energy needed to raise the temperature of one gram of water, at a specific temperature, one degree Celsius. 1000 calories is a kilocalorie.

A BTU or British Thermal Unit is the amount of energy needed to raise one pound-mass of pure water at a specific temperature one degree Fahrenheit.

kilowatt-hour, horsepower-hour
Both are units commonly used to measure cumulative power or the total energy consumed by a mechanical or electrical system. Use the formula:

energy = power x elapsed time.

Note: Because of round-off errors, converting from very large units to very small units or vice-versa may not be accurate (or practical). Conversion factors can be found by converting a quantity of 1 unit to another unit several steps above or below the first. You may need to string several conversion factors together to find the factor from a very large unit to a very small unit, and then you can use a calculator with sufficient digits to find your answer.