Unit 1: What is Energy?

Section C. Measuring and Quantifying Energy


Measuring and Quantifying ENERGY

Just as there are many forms of energy, there are different ways to measure and quantify these forms. In science, work and energy are commonly measured in joules. One joule is the amount of energy it takes to lift an object that weighs one Newton a one-meter distance. A Newton is the metric unit for weight and is comparable to the weight of an apple. (1 lb = 4.45 Newtons)

In our everyday lives, other energy measurements are more familiar to us than joules. Some of these units of measurement include Btuscalories, and kilowatt-hours. Definitions of these and other units are found below. 

It might seem confusing to have so many different units of measurement for energy. The good news is that one unit can be converted to another. (See Energy Conversion and Resource Tables).

Definitions:

British thermal unit - (abbrev. Btu) 

1. A unit of energy equal to 1,055 joules or 252 calories. 2. The amount of energy needed to raise the temperature of one pound of water one degree Fahrenheit.

Calorie (abbrev. cal; pl. calories; also small calorie):    

1. A unit of energy often used when measuring the energy content of food. One calorie equals 4.187 joules or 0.003969 British thermal units (Btu). 

2. The amount of energy needed to raise the temperature of one gram of water one degree Celsius. 

3. Units related to the calorie:

        • Food calorie (abbrev. Cal, kcal; also Calorie [written with a capital C], Kilocalorie, Large calorie): A unit of energy equal to one kilocalorie (see next entry). The food calorie is often used when measuring the energy content of food.
        • Kilocalorie (abbrev. Calkcal; also Calorie [written with a capital C], Food calorieLarge calorie): 1. A unit of energy equal to 1000 calories, 4,187 joules, or 3.969 Btu. 2. The amount of energy needed to raise the temperature of one kilogram of water one degree Celsius. 

Foot-pound (abbrev. ft-lb; pl. foot-pounds): 

1. A unit of energy equal to 1.356 Joules or 0.3238 calories.

Joule - (abbrev. J; pl. Joules): 

1. A unit of energy equal to 0.2388 calories or 0.0009481 Btu.

Kilowatt-hour (abbrev. kWh; pl. Kilowatt-hours): 

1. A unit of energy equal to 3,413 Btu or 3,600,000 joules. 2. An amount of energy that results from the steady production or consumption of one kilowatt of power for a period of one hour. The kilowatt-hour is generally used to express electrical energy consumption.

Therm - (pl. Therms

1. A unit describing the energy contained in natural gas. One therm equals 100,000 Btu. See British Thermal Unit.

Measuring and Quantifying POWER

Power is defined as the rate at which energy is transferred or converted per unit of time. It is also the rate in which work is done. Some units of measure for power include horsepower and Watt

One way to help distinguish between energy and power is to think of two people each eating an apple pie. One person eats their pie faster than the other. They both ate the same amount of pie (they consumed the same amount of energy), one just ate the pie at a faster rate (the faster one was a power eater!). 

Like units of energy, units of power can be converted to another. (See Energy Conversion and Resource Tables).

Definitions:

Horsepower (abbrev. hp): 

1. A unit of power equal to 550 foot-pounds per second or 746 watts. 

Watt (abbrev. W; pl. Watts): 

1. A unit of power equal to the production or use of one joule of energy per second.

2. Units related to the Watt:

        • Kilowatt (abbrev. kW; pl. Kilowatts): A unit of power equal to 1,000 watts. 
        • Megawatt (abbrev. MW; pl. Megawatts): A unit of power equal to 1,000,000 watts.


To help you better understand how to measure and quantify energy, participate in the Activity: People Power.



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