Project 3.1.4 Measuring Energy
Introduction
Wind power is a popular option for producing electricity. Power companies are not only harnessing wind through wind farms, but individuals are also constructing wind turbines on their own property. Often the power that people produce with their own wind turbines exceeds what they need. Most states allow net metering, which means that the excess electricity goes back into the power grid. Not only does it return to the grid, but the electric utility pays retail price for the electricity infused into the grid. If this were your house, you might receive a check from the electric company instead of a bill each month.
Power and work are important concepts that impact the engineering design of items ranging from racecar engines to elevators to power plants. High-power cars (high-horsepower) are able to accelerate very quickly and go very fast. Elevators in skyscrapers require enough power to lift many people quickly in order to avoid long elevator waiting lines. Power also plays an integral role in the production of electricity from wind turbines.
Work is measured in Joules (J) and is defined as force acting over a distance, or:
Work = Force x Distance
W = F x D
Joules = Newton-meter
In this activity work will be done lifting a weight. The force term equals the weight in Newtons, and the distance term equals the height lifted in meters.
Power is measured in Watts (W) and is defined by how fast work is done, or:
Power = Work ÷ time
P = W/t
Watts = Joules/seconds
To help distinguish between work and power, think of two people eating a piece of pizza. One person eats the pizza faster than the other. They both eat the same amount of pizza, so they do the same amount of work. One eats at a faster rate, the power eater.
In this activity you are working for Wind Power Designs, an engineering design firm that works with wind energy. Your city wants to use wind power instead of coal to make energy because they are worried about air pollution. The city has hired you to design an efficient wind turbine. The firm (our class) has been split into several engineering teams (student groups). Each engineering team will design and test a slightly different design so that the firm can present the most efficient design to the city. You will calculate power and work by measuring force, distance, and time for your team-built wind turbine.
Equipment
· PLTW Gateway notebook
· Pencil
· Computer with Internet and CAD program access
· Wind turbine base
· Nacelle for wind turbine (1 per group)
· Blade materials (balsa or bass wood, cardboard, Styrofoam, paper plates, etc.). Do NOT use metal or sharp-edged material. Blades tend to spin very fast and can easily cut you.
· Dowel rods
· Tape
· Hot glue
· 24 in. string
· Weight (1 per group)
· Box fan
Procedure
The engineering teams in your class will brainstorm and research possible solutions for the wind turbines, then discuss these options. Each team will sketch, prototype and test a different option. Each member of the team should record the design process ideas, sketches, and notes in their engineering notebook or use the templates provided by your teacher.
Safety Note:
· Do not make blades out of metal or sharp-edged material, as these could cause injury while spinning during testing.
· It is important to wear safety goggles when testing blades.
1. Each engineering team will brainstorm, research, and create annotated sketches using CAD software of their wind turbine ideas. Use the Internet and other available resources to learn about methods used to capture wind.
2. Present your ideas to the Wind Power Designs firm. The project manager will coordinate the teams so that each team creates and tests a different model. Record the criteria and constraints that your team must meet on your design brief.
3. As an engineering team, build your wind turbine model. Remember to record the process in your engineering notebooks.
4. Test your design and record in your engineering notebook:
· Mass of the weight you are using in kilograms
· Distance the weight is travelling in meters
· Time it takes for the weight to travel that distance
5. Use the Measuring Energy Data Table to calculate the work and power created by your wind turbine. Remember, to calculate force you must multiply the mass by gravity (~9.8 N/kg).
6. Make adjustments if necessary to improve your model. Make sure your wind turbine design still meets your criteria and constraints. Document these changes in your engineering notebook.
7. Retest your design, record values, and calculate work and power.
8. Make adjustments if necessary to improve your model. Make sure your wind turbine design still meets your criteria and constraints. Document these changes in your engineering notebook.
9. Retest your design, record values, and calculate work and power on the Measuring Energy Data Table
10. When your engineering team feels that you have accurate figures to present to the firm and the most efficient wind turbine that meets the specifications, prepare necessary documentation to present to Wind Power Solutions.
11. Present your solution to the class, justify your design changes, and describe how the wind turbine efficiency improved.
© 2011 Project Lead The Way, Inc.
PLTW Gateway – Energy and the Environment Project 3.1.4 Measuring Energy – Page 1
Measuring Energy Data Table
Speed = Distance / Time
Force of gravity = 9.8 m/s2
Output Force = mass x gravitational acceleration
Work is measured in Joules (J) and is defined as force acting over a distance
Work = Force x Distance W = F x D Joules = Newton-meter
Power is measured in Watts (W) and is defined by how fast work is done
Power = Work ÷ time P = W/t Watts = Joules/seconds
Washer Count / Total Washer Mass(Kg)
(divide grams by 1000) / Distance (m)
(cup travelled) / Time (sec) / Speed (m/s) / Force of Gravity / Output Force (N)
(gravity x mass) / Work (J)
(output force x distance) / Power (W)
(work/time)
Trial 1
Trial 2
Trial 3
Average
© 2011 Project Lead The Way, Inc.
PLTW Gateway – Energy and the Environment Project 3.1.4 Measuring Energy – Page 1
Conclusion
1. Explain the difference between work and power.
2. A wind turbine produces 200 kW of electricity. How many 100 watt light bulbs can this wind turbine light?
3. A bodybuilder loads a bar with 550 Newtons (~125 pounds) of weight and pushes the bar over her head 10 times. Each time she lifts the weight 0.5 meters. How much work did she do?
4. If she lifts the bar 10 times in 20 seconds, how much power did she use?
5. How did math help you determine the amount of watts your turbine produces?
6. Why do engineers use math?
7. Describe the blade design for a wind turbine that you would choose. Why did you choose this design?
8. Describe three environmental concerns associated with wind turbines.
9. Firms often divide into engineering teams to complete a project. List advantages of working in an engineering team.
© 2011 Project Lead The Way, Inc.
PLTW Gateway – Energy and the Environment Project 3.1.4 Measuring Energy – Page 1