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For my science project I am testing to see the most efficient way to generate geothermal energy using a pinwheel and boiling water. The dependent variable is how many times the pinwheel spins in a full circle in a 20 second time span. How many variables do you think are necessary for a decent grade? Is one data table enough or should I have more? What type of graph should I use. Also, could you be sure to finish this before my project is due? The date is January 22, 2013. Thanks!
Answer 1:

I suggest you first look at some designs. Wikipedia is a good place to start - it is not the only place to look, but it can help. See

geothermanl-electricity

There is a good schematic here:

alternative- energy

But...then I found exactly what I think you're supposed to be doing here:

science- projects

Scroll down the page a bit, and you'll find this description of how to do your experiment:

Geothermal Energy Part 1: Setup
Have a student simulate a geothermal energy plant where scientists gather energy from the Earth's heat. Fill a kitchen pot halfway with water. Place two layers of aluminum foil on the pot so that steam cannot escape. Punch a 1/8-inch-wide hole through both layers of foil in the center of the pot. Take an opened aluminum can, such as an old green bean can, and place it with the opening face down. Punch a 1/8-inch- wide hole on one side using a hammer and nail. Punch an identical hole on the opposite side. Place a ruler on the side of the can, flush with the bottom, and attach it using a rubber band. Heat the pot of water to boiling over medium heat. Make a dot with a permanent marker on the back of a pinwheel, placing the dot at the outside edge so that rotations can be counted.

Geothermal Energy Part 2: The Experiment
Heat from the Earth naturally rises to the surface.

When the pot of water is boiling, place the aluminum can on the foiled pot over the hole. Hold the pinwheel above the can and measure its rotations for 20 seconds. Do this three times for 20 seconds each. Make a mark on the ruler at the height where the pinwheel is held. Take the can off the ruler, hold the ruler on the top of the pot, and place the pinwheel at the same height as before. Measure the rotations for 20 seconds, record your findings and repeat two more times. Take the pot off the heat, allow it to cool and refill the pot with water so that it is half full. Replace the aluminum foil layers and punch eight holes 1/8th of an inch through both layers of foil around the edges of the pot. Repeat the experiment and analyze the results.

First of all, if this is the experiment you're supposed to do, I'd say DRAW A PICTURE OF IT FIRST so you can visualize what you're supposed to do.

Second, I'd ask: Why in part 1 do they say to poke 1 hole in the foil, and in part 2 they say to punch 8 holes in the aluminum? Why 2 holes in the can, on opposite sides? Why not just one hole on one side?

To answer your question as to how many graphs, well...a lot. Let's think it through:

What are the variables in this experiment?
2. Height of pinwheel
3. Number of holes in the can
4. Number of holes in the foil

You might also say that the mass of the pinwheel is a variable. What would be the difference, do you think, of a lighter or heavier pinwheel? One that has more mass towards the center, or more towards the outside? I would say, look up some pictures on the internet to see what design geothermal engineers have used. Then select your pinwheel design.

Next, why do you think they say to fill the pot half full? What could be the advantage of using more or less water? You might just decide that you are not going to vary the amount of water. I'd state that in the introduction to my write up...

For height of pinwheel: I'd say, first get a feeling for how height of pinwheel affects the rotations. Blow a stream of air out your mouth at the pinwheel, and move it up and down, so that your air stream hits the edge to the center. The place on the wheel where the stream of steam hits may affect the speed - that is, hit closer to the end of a blade vs. hitting closer to the center.

This is called torque: if you push on a wheel closer to the edge, you have more leverage, because you have more distance to the center of the rotation. Try this - if you want to open a door, do you have to use more force if you push closer to the hinge, or closer to the outside? So, for the same force, would the door open faster if you push closer to the hinge or the outside?

I would say that you want to start by having the steam hit the pinwheel at the edge of the blade, then move the pinwheel up (or down) in half-inch increments until the steam is hitting it in the center. You don't have to test any more heights, because the other side is just the mirror image of the first side, so you would expect the same results as you go out towards the other edge.

Last, number of holes. They want you to start with 1 hole in the foil and 2 holes in the can. I'd start with 1 hole in the foil and 1 hole in the can. Then increase the number of holes in the foil while keeping only 1 hole in the can. Then I'd punch a second hole in the can, take new foil, and do the whole thing again - starting with 1 hole in the foil, and increasing to 8.

So, how many graphs?
Let's say, water level is fixed at half. You'll have to check and make sure the level is constant, so you'll have to add water and get it back up to a boil in between changing the other variables.

Note from ScienceLine coordinator:
Please go to the next field (Answer 2) to read the rest of this answer


Answer 2:

In making a graph, you have to decide on an independent variable, and a dependent variable. So, you have THREE variables that you're changing: holes in the can (one or two), holes in the foil (1 to and height of the pinwheel (steam hitting edge to steam hitting center - maybe you can divide this into 5 increments, depending on the size of your pinwheel. The easiest way to do this would be for each combination of holes (can and foil) you measure the speed of the pinwheel at 5 heights

So, you'll have to take a bunch of data
1 can hole
1 foil hole
5 pinwheel distances
5 speed measurements

1 can hole
2 foil holes
5 pinwheel distances
5 speed measurements
etc, up to 8 foil holes.

Then make 2 can holes, and repeat everything. That comes out to 16 graphs.

By separating the variables in this way, you should be able to come out with a statement that suggests the optimal combination for the fastest speed of the pinwheel.

A really good experiment ends with a suggestion for further research. What questions does your experiment lead you to? Would you suggest trying a heavier or lighter pinwheel?

Good luck, and please let me know how it comes out!

All the best,


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