### Introduction

People often use the words power and energy interchangeably, when in fact these two words mean very different things.

Imagine if people used the words “kilometers per hour” and “kilometers” interchangeably. That would be very confusing! It would sound like this: “How fast can you ride your bike?” “About 5 kilometers.” This is basically what we are doing if we use power and energy to mean the same thing.

Power is a rate–just like meters per second, miles per hour, and gallons per minute are rates. Power is the rate at which energy is transferred or work is done. It can be calculated using the equation

$\text{power} = \frac{\text{amount of work done}}{\text{how much time it takes}}$

The base unit of power is the watt (W), which is equal to one joule per second (1 W = 1 J/s).

We can think of energy, on the other hand, as a quantity–just like gallons and meters are quantities. Energy refers to the amount of energy transferred or work performed. The base unit of energy is the joule (J). You can calculate energy by rearranging the power expression in the following way:

$\text{amount of work done} = \text{power} \times \text{how much time it takes}$

As an example, let’s say you leave a 12 W light bulb on for 10 seconds. Using the expression above, you can calculate the amount of work:

$\text{12 W} \times \text{10 s} = \text{amount of work done}$ $\text{12}\frac{J}{s} \times \text{10 s} = \text{120 J}$

In the United States, a common unit of energy is the watt-hour (Wh) or kilowatt-hour (kWh). With small classroom wind turbines and solar panels, we sometimes use the unit “milliwatt-second” (mWs), which is equal to one thousandth (1/1000) of a joule and could also be called a millijoule.

In this experiment, you will explore power and energy. You will learn how power and energy are related to each other. You will use this knowledge and the data-collection software to measure the power and calculate the amount of electrical energy generated by a small wind turbine.

### Objectives

• Understand the difference between power and energy.
• Calculate the amount of electrical energy generated by a wind turbine during a time period.