First - You know which blade design produced the most voltage and at what angle. You also know if that set ALWAYS produced more voltage or if your data overlaps at the other angles
Second - You know if your blades followed the trend we noticed in the lab. The most voltage was often produced by blades tilted at a small angle. (For just about every blade design)
As you think about WHY your two sets of blades worked the way they did, keep these things in mind:
Putting the blades at a small angle increases the area that the wind is hitting, increasing the force that is helping to spin the generator.
but.....
When the hub spins, the blades have to work to move sideways through the air because they produce drag (air resistance/friction).
and.....
Blades that are tilted at larger angles have to push through more air so they produce even more drag than small angles.
and.....
Newton's 2nd law says it will take more force to spin larger and more massive blades, but if they get spinning, they will have more MOMENTUM to help fight through the drag of air resistance.
and.....
The tips of longer blades have to travel around a larger circle than the tip of smaller blades.
Start your draft in class once you are done with your graph.
Paragraph 1 - Describe the experiment, Summarize the results and explain your thinking about them.
- Describe the variable you and your partner tested and the design of your blades.
- Restate your hypothesis.
- Which set of blades was able to produce the most voltage and at what angle?
- Did this set of blades produce more voltage at ALL the angles we tested? If not, which angles did the other set of blades "win"?
- Was your hypothesis supported? Did the variable you changed about the blades have the effect you thought it was going to or did the results surprise you?
- Use what you know about Forces, Drag, and Newton's laws of motion to try to explain why one set of blades was able to spin faster and produce more voltage than the other.
Paragraph 2 - Data Analysis. Describe patterns in the data and use calculations to compare the data, along with your own observations, to explain how clear and convincing your data is.
- Is there a clear difference between the amount of voltage your two sets of blades were able to produce or did they produce almost the same voltage?
- How big was the difference between the two sets of blades and the MEAN voltage they were able to produce at the angles we tested? (Use Subtraction to compare!)
- Which set of trials had the HIGHEST range and how high was it?
- Do you think the data is consistent enough for us to trust or are there patterns that make you skeptical?
- What were some of the issues with our equipment that you and your partner encountered when running the tests that might make us trust your results a little less?
Paragraph 3 - What are your thoughts on how we could improve or change this experiment?
- What variables were the hardest to control when running this experiment?
- Were there problems with your blade construction?
- How could we fix any problems we had with our equipment to make the test more fair?
- What other blade designs would you be interested in testing if we were to start this process over again?
- What other variables besides the blade design could we test to see how much they affect the voltage a turbine can produce?
Your conclusions tell the story of the experiment and what you were thinking along the way.
Be sure to use specific language to clearly explain yourself and include the evidence and FACTS that you think are important to support your ideas and opinions.
Here are some examples of how to write about the results:
"My partner and I decided to test the overall size of the blades in the turbine. We used a thick cardboard and made our blades rectangle shaped. The control blades had an area of 50 square centimeters and the experimental blades were larger with an area of 90 square centimeters. My hypothesis was that the larger blades would spin faster because.....(thinks about Newton's laws and where the air is going)"
"When you look at the results you can see that the larger blades spun faster at 40° and produced 0.025 more volts at that angle. The smaller blades produced more voltage at every other angle. The most voltage the small blades produces was 0.895 volts at 15°which is 0.090 more volts than the large blades were able to produce. This is not a big difference, but I think it is a clear one because all three trials from the small blades were had more volts than any of the trials with the long blades. The large blades best angle was also 15°."
Our data was mostly consistent with small ranges of only a few thousandths of a volt. The largest range in a set of trials was our large blades at 30° with a range of 0.125 volts. If we had more time i would have retested that angle. I think that we might not have used the protractor correctly and one of the blades might have been at a different angle.
We noticed that our generator and tower wobbled whenever we tested our larger blades. This could be because....
One of our smaller blades was damaged during the testing and we had to re-glue the dowel rod two times. This might have changed how much the blade weighs.
If we started over I would like to design blades that have a curved edge. I also noticed that some other blades had shorter dowel rods and I think that might be interesting to test as well.
