Physics Lab B/C

[ichaelm]

Just finished optimizing our design for nationals. I just wanna say that at a certain point, once you've taken off all the excess mass you can, mass isn't really a factor anymore. Especially as high speed, the bigger factor becomes aerodynamics, drag, and turbulence. It's a good idea (in my experience) to taper the leading and trailing edges of the blades to decrease drag and turbulence. The entire surface area of the blades should be aerodynamically useful; don't leave the center flat. Also, stability is key. If it makes too much noise, it's probably unstable. Noise (vibration) is wasted energy. Also unless you have some wicked design that intentionally morphs with different wind speeds to make it better, which i have never seen but it would be amazing, bending is generally bad. Finally, don't make the same mistake we made last year at states. We got a score of 0 because our blades were just slightly touching the back of the setup. We ended up with 3rd overall, and our place in physics lab was bigger than the difference between us and nationals. Don't risk it. On the other hand at nationals there's nothing to loose!

[E Edgar]

Here are some results from C-division nationals if anyone is interested.

The test was very easy and so basically the best blades won. The way they had it set up was that there was a high speed fan and a low speed fan. At each fan, they would record your reading for that speed. The fans were not particularly fast and neither were the motors. Of course, that doesn't matter since everyone had the same setup.

Our readings were (these could be slightly off) 1628mV on high and 1287mV on low. We were the very last team to test and were told that our blades were 2nd but very close to Troy's on high power and the fastest in the nation on low power. We took 2nd overall. We got the impression that the 3rd place team was significantly slower but perhaps we were mistaken.

I would also like to say that we got the results we did without any outside design help and so definitely anyone who was motivated enough could have done as well as we did. I molded basswood blades on a metal pipe to get the right curvature. My approach was highly experimental: I changed one variable at a time until I basically got what seemed to be a near-optimal design. Once I had a really good design, I molded several blades to get 2 that were close to identical. In all, I probably molded about 40 pairs of blades to find the design I used and about 10 to get 2 blades that were identical. I learned a huge amount along the way just by observing what worked and by thinking about the physics that determine how the blades function.

[mister]

Division B Physical Science Lab

Our high speed voltage was 2160mV and our low speed voltage was 1166mV. How were some of the other scores for the fan voltages in Division B?

--We got Third in the Nation!!!--

[Littleboy]

can you put pics on the image gallery for others to see. thanks and have a nice day

[ichaelm]

Great job guys!!! In division B, we got 8th, with a high of about 1830 and a low of about 900. We were the fastest in PA (by a lot; we know the guys at Strath Haven who got 2nd place), so we didn't change our design much since then. The test was kind of easy, but there were some weird parts, like that thing about that energy bill. I may eventually post pictures or specifics about my design, but I'll have to talk to some people first. Also, it seems that there were 7 designs out there that would be more helpful than mine! Congratulations guys!!!

[nejanimb]

Here are some results from C-division nationals if anyone is interested.

The test was very easy and so basically the best blades won. The way they had it set up was that there was a high speed fan and a low speed fan. At each fan, they would record your reading for that speed. The fans were not particularly fast and neither were the motors. Of course, that doesn't matter since everyone had the same setup.

Our readings were (these could be slightly off) 1628mV on high and 1287mV on low. We were the very last team to test and were told that our blades were 2nd but very close to Troy's on high power and the fastest in the nation on low power. We took 2nd overall. We got the impression that the 3rd place team was significantly slower but perhaps we were mistaken.

I would also like to say that we got the results we did without any outside design help and so definitely anyone who was motivated enough could have done as well as we did. I molded basswood blades on a metal pipe to get the right curvature. My approach was highly experimental: I changed one variable at a time until I basically got what seemed to be a near-optimal design. Once I had a really good design, I molded several blades to get 2 that were close to identical. In all, I probably molded about 40 pairs of blades to find the design I used and about 10 to get 2 blades that were identical. I learned a huge amount along the way just by observing what worked and by thinking about the physics that determine how the blades function.

A well-deserved congratulations to you! That's very impressive. Our turbine didn't stack up: high 800s on high and mid 600s on low. We think we did very well on the test, but, as you said, it was extraordinarily easy... which I thought was a real shame. We got 18th, which really isn't that bad, but I was disappointed by the test they gave us. We spent a whole year learning all kinds of physics and preparing an extremely comprehensive binder, and we needed neither our physics knowledge nor anything in our binder - it was just about all common sense. We knew our blade setup wasn't going to be the best, so we would need a harder test that we could do well on if we wanted a shot to do well... and that was absolutely not what we got.

One thing: One question I was very confused about was the one about what would happen if the average wind velocity in a wind farm doubled and how would the average available kinetic energy in the air change. I was pretty sure it's Kinetic Energy = 0.5 * rho * area * velocity^3, which means that if the wind speed doubles the kinetic energy should increase by a factor of eight... but the multiple-choice options were 2x, 3x, 4x, 5x, and 6x. We thought that maybe we were missing something and that the word "average" in the problem should trip us off to use rms speed or something, but that didn't make sense either, so we ended up just putting 6x. Did anyone else notice this issue, or am I wrong in the answer I got?

[E Edgar]

One thing: One question I was very confused about was the one about what would happen if the average wind velocity in a wind farm doubled and how would the average available kinetic energy in the air change. I was pretty sure it's Kinetic Energy = 0.5 * rho * area * velocity^3, which means that if the wind speed doubles the kinetic energy should increase by a factor of eight... but the multiple-choice options were 2x, 3x, 4x, 5x, and 6x. We thought that maybe we were missing something and that the word "average" in the problem should trip us off to use rms speed or something, but that didn't make sense either, so we ended up just putting 6x. Did anyone else notice this issue, or am I wrong in the answer I got?

We were confused by that question as well. It seems strange that the question asked about kinetic energy when it is power that is the important quantity. In the end, we assumed that they wanted us to use the (incorrect in this situation) equation KE=.5mv^2 and therefore said the kinetic energy would be 4 times as much.

[walkingstyx]

We actually used the exact same thought process as you nejanimb, and eventually justified it by saying that the average of the squares is less than the square of the averages, and the difference in wind speeds is great enough to maybe account for the difference between 6 and 8, but I think there's a good chance that the question was just wrong.

[nejanimb]

Agreed - given the overall quality of the test and questions.... it was probably just wrong. Urgh. I have a feeling you went with the right reasoning, E Edgar, and he probably was just looking for v^2. Other other one we were very unsure about was the question "What type of energy is the event supervisor measuring when he takes a voltage reading?" My partner decided to go with potential energy, since the "voltage" part of it does mean that it's a measurement of electric potential, but I wonder if the test wasn't being strange on this one too - kinetic energy of the blades, or even "efficiency" since it's how much energy of the incident wind can be captured?

Ah well - nothing to do about it now. I do think it's a real shame though - the kinds of tests that can be generated for those rules *could* have been very cool...

[Illusion]

What did you guys say for the question asking about what voltage was measuring (PE, KE, Electric Energy, Efficiency, or All of the Above)?

I'm pretty sure that all of the answers were wrong.

We ended up saying 4x for the wind energy one also (because we thought the test writer may have just been talking about the additional KE of the wind). We originally got 8x too.

[E Edgar]

Other other one we were very unsure about was the question "What type of energy is the event supervisor measuring when he takes a voltage reading?" My partner decided to go with potential energy, since the "voltage" part of it does mean that it's a measurement of electric potential, but I wonder if the test wasn't being strange on this one too - kinetic energy of the blades, or even "efficiency" since it's how much energy of the incident wind can be captured?

Ah well - nothing to do about it now. I do think it's a real shame though - the kinds of tests that can be generated for those rules *could* have been very cool...

We had a debate during the test about that question as well. In the end we went with potential energy for the same reason you did.

Yeah, the questions just felt misleading and trivially easy after the excellent test that we took at state.

[ichaelm]

I'll know by wednesday what I can do about posting pictures. I'm really excited to see what some of the best at nationals were like! If physics lab is not an event next year, why don't all the people here post some pictures? I'm dying to see what we were beaten by XD

[Littleboy]

It's not an event for who next year(B, C, both)?
Congrats to all for the work that finnaly paid off

[ichaelm]

I meant "If." I don't know.

[Flavorflav]

One thing: One question I was very confused about was the one about what would happen if the average wind velocity in a wind farm doubled and how would the average available kinetic energy in the air change. I was pretty sure it's Kinetic Energy = 0.5 * rho * area * velocity^3, which means that if the wind speed doubles the kinetic energy should increase by a factor of eight... but the multiple-choice options were 2x, 3x, 4x, 5x, and 6x. We thought that maybe we were missing something and that the word "average" in the problem should trip us off to use rms speed or something, but that didn't make sense either, so we ended up just putting 6x. Did anyone else notice this issue, or am I wrong in the answer I got?

That's the power formula. Energy is just 1/2 mv^2.