Teachers TryScience

The lesson presented here focuses on the engineering design process and its use in identifying a question (solving a problem), developing a design or change in design, testing that design, observing and collecting data, analyzing the data recorded from the experiment, and forming a conclusion to perform another round of design. In this case, we are attempting to maximize the voltage obtained from a wind-driven turbine through the use of several experimental designs.

You may want to review the following multimedia presentations to learn more about STEM and the engineering design process.

• What is STEM Education

• What is Engineering

Instructions for creating a wind-powered electrical generator

The teacher should be sure to create a wind generator and test out the procedure prior to the implemenation of the lesson. The following instructions, which include the video below, are a suggested baseline approach to teachers in preparing the lesson and building their personal turbine/generator/voltmeter apparatus.

• Creating a Wind-powered Electrical Generator

Cut a two-centimeter length of a wide mouth straw and insert a skewer into the side of the straw length such that the end of the skewer comes out of the other side. Make sure that an even length of skewer is sticking out of both sides of the straw. Repeat this procedure with one more skewer, inserting the skewer perpendicular to the first skewer. The two-centimeter length of straw should now form an axis, it’s center being “crossed” by the skewers. In all, this should form a turbine without blades attached to the skewers.

Using the pencil and ruler, draw a blade on the index cards. As the blades are drawn, keep in mind that the goal of the activity is to maximize the voltage that will be read on the voltmeter. To achieve this, the shaft of the motor/generator must spin fast. Hypothetically, the more the blades can “catch the wind”, the faster the turbine will spin thus generating a larger current and, therefore, voltage. Once the blades have been designed, tape them to the skewers forming the wheel of the turbine. Remember, to get the turbine to spin quickly, they should tape the blades to the turbine in such a way that wind from the hairdryer will hit the blades with a great deal of force or such that the surface area and the angle of the blades will be maximized.

Instructions for Setting Up the Generator and Voltmeter and Adhering the Propeller (Turbine) to the Generator

Using masking tape, tape a ruler to a desk making sure that at least 5 cm of the ruler is extended off of the table. With the rubber band or electrical tape, attach the toy motor/generator to the part of the ruler that is extended off of the table making sure the shaft of the motor/generator is suspended off the edge of the ruler. This will give some distance between the turbine and the table such that the blades of the turbine do not hit the table. As a practice test, the instructor should attach the turbine that they he or she creates to the shaft of the generator to ensure that the distance between the blades and the table are sufficient to prevent any interference of the blade movement by the table. Wires should be connected from the generator to the voltmeter such that a voltage is registered when the generator’s shaft is rotated. The clay should be placed into the wide mouth straw (central axis of the turbine) to allow the turbine to “stick” to the shaft. By blowing a hairdryer across the turbine, it should rotate, consequently registering a voltage on the meter.

Introductory Discussion Talking Points

The teacher should approach the introduction of the lesson the way they deem most beneficial to their students. However, the key is to allow the students to become active participants in their own learning using prior knowledge, experience and self-inquiry.

Engage the students in a discussion in which they express what they know about wind, electricity and how wind can be harnessed to power an electrical generator. The following video may inform your teaching:

• KWL Video

A discussion of how fossil fuels generate electricity should take place. Emphasis on the use of heat and turbines to actuate electrical generators should be emphasized. This can also be a research activity as a preamble to the design activity. Students can identify the kind of fuel and generation system being used in their community, perhaps organizing a field trip to the power generation plant.

The following are points to cover during the introductory discussion:

• Gases and their properties (air in particular)
• The nature of electricity and electrical generators
• A brief discussion of fossil fuels, their depletion and how they impact the natural environment
• Alternative fuel sources (wind in particular)
• Wind turbines, their design, and how they function. You can share the following Wind Turbine Animation with students as a way to frame this part of the discussion:

Wind Turbine Animation

• The fact that wind turbines can transfer mechanical energy into electrical energy. You can have students compare/contrast steam generated by a fossil fuel boiler and wind as energy source. (NOTE: The students will conduct experiments to find out HOW this transfer takes place.)

Discussion Following Procedure Part 2: The Competition Round 1: What Effect Does Temperature and Pressure Have On Gases?

After part 2 of the procedure (below), start a new discussion in which the students are asked to consider the behavior of air (which is a gas) and how wind is formed. Ask students what affects gases and their movement. After a few responses, discuss how temperature and pressure affect how gases behave.

Refer to the attached document (What Effect Does Temperature Have On Gases?) for a demo and in-class experiment that can be used to further the discussion.

Consider what happens to warm air as it rises. When a gas is warmed, the molecules comprising the gas are not as closely packed together. As temperature decreases, however, the molecules come closer together. This closeness of molecules reflects the density of the gas as given by the equation:

Density = Mass/Volume

Thus, as the volume increases, the density decreases and vice-versa.

The effects of temperature and pressure can be combined and be described by the following equation.

PV = nRT where:

P = Pressure

V = Volume

n = a given number of air molecules

R = Ideal gas constant 8.3145 J/ (K mol)

T = Temperature

OR

P(M/D) = nRT where:

M/D is Mass/Density and is substituted mathematically for volume.

Ideally, you can work in partnership with their math teacher to have the students work on some sample calculations before they do this experiment. This will make the connection more salient

Given that the students now have a familiarity with air and how it is affected by temperature and pressure, ask them how they think wind forms. Wind is formed when air moves from one place to another due to differences in temperature and pressure. Other things can affect this movement as well. Ask the students what they think could affect wind movement and what affects wind can have on different areas of the earth (e.g., continents and oceans). Some examples of things that affect wind movement include landscapes (e.g., mountains act as an obstacle), climate, other wind parcels (fronts) and the earth’s rotation.