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Sunday, January 29, 2012

MEASUREMENT OF ENERGY

In the previous discussion (Characteristics of Energy Matter), we developed the concept of energy. We now must be able to measure and quantify it, using a standard set of units. Worldwide, two systems of units of measurement are commoly used today: the Metric System (Systeme International) and the British System. The units of energy described in these systems are derived from a technical definition of energy used by physicists. This definition suggests that energy can be represented by the following simple equation:

Work = Force x Distance

Similar to the definition given in the previous topic, physicists view energy as the ability to do work. However, they define work as a force applied to some form of matter (object) multiplied by the distance that this object travels. Physicists commonly describe force with a unit of measurement known as a newton (after Sir Isaac Newton). A newton is equal to the force needed to accelerate (move) a mass weighting one kilogram one meter in one second in a vacuum with no friction. The work or energy required to move an object with the force of one newton over a distance of one meter is called a joule.

Some other definitions for the energy measurement units that you may come across in this textbook are as follows:
  • Calorie - equals the amount of heat required to raise 1 gram of pure water from 14.5 to 15.5° Celsius at standard atmospheric pressure. 1 calorie is equal to 4.1855 joules. The abreviation for calorie is cal. A kilocalorie, abbreviated kcal, is equal to a 1000 calories. 1 kilocalorie is equal to 4185 joules.
  • Btu - also called British thermal unit is the amount of energy required to raise the temperature of one pound of water one degree Fahrenheit.
  • Watt (W/m2 or Wm-2) - a metric unit of measurement of the intensity of radiation in watts over a square meter surface. One watt is equal to one joule of work per second. A kilowatt (kW) is the same as 1000 watts.

CITATION: Pidwirny, M. (2006). "Measurement of Energy". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.