Siphon Experiment: Testing Bernouilli’s Principle

For my Science course this year, we were required to do a science fair experiment, complete with a poster board and research paper. I was chosen by my school to become a Broadcom MASTERS National Science Fair Nominee. I will be sharing the highlights of the process, and I hope to be able to inform the reader on how to successful go through the research and experimenting process, and more specifically, to inform the reader on my topic: Siphons.

• Paper cups
• Duct Tape
• Ruler
• Funnel
• Tubing .00365m (.25inch) [inner diameter]
• Large Pipette
• Green coloring
• Bowl and pitcher
• Water
• Hot glue gun w/ glue
• 1 cup, ½ cup, measuring cups
• Window ducting unit
• Laptop 
• Custom 3D models
• 3D printer + Filament
• Stool, cookie sheet, oven shelf (base)
• Wooden Plank
• Blow Dryer
• Stopwatch + camera (phone)

(the bolded materials are ones that are actively used in the experiment, the rest are setup.)

For the first part of my science fair, I wrote a research paper on my topic. I condensed my research into the essentials for my poster, and that is what I will be sharing in the text here. I will attach images of my paper in case anyone wants a more in depth overview of the subject.

• A siphon is a reservoir of liquid connected to another reservoir at a lower point by an inverted “U” shape.
• Once the water reaches the highest point, the siphon flow will continue.
• This allows water to flow over an edge without any energy input.
• The most popular uses of a siphon are to empty above ground pools, as it can get water out easily, and as the flushing mechanism in some toilets.
• Siphons work due to a mixture of gravity and pressure. As the liquid drains down one arm, a partial vacuum is created at the top, and water is pushed up the other arm to fill it. This creates a continuous cycle and flow of water.
• Siphons are hypothesized to work in accordance with Bernoulli’s principle which states that the less pressure there is within liquid flow, the faster the flow will be.

The reason that I chose this experiment is because I wanted to test for myself whether siphons actually worked with the Bernoulli Principle as theorized. If the height difference is increased, the length of the section going downwards is increased as well. With that, because a siphon starts with water filling it, there will be more water being pulled downwards through a larger section, creating less pressure at the top. If Bernoulli’s principle is at play here, this should cause the siphon to go faster. Because it is the hypothesis of leading scientists, I decided to side with them and make my hypothesis that it would be used.

Independent Variable: The height difference between the two openings of the siphon.

Dependent Variable: The speed of the water

Hypothesis:

The greater the distance between the two siphons, the faster the speed will be.

Here is my complete setup as I wrote it in my lab write-up. In the diagram you can see what the final product looks like.

1. 3D print all parts needed
2. Tape the oven shelf to the cookie tray, and tape the cookie tray to the stool.
3. Tape window ducting to cabinet side.
4. Put stool against window ducting.
5. Tape one cup to the oven shelf.
6. Attach the other cup to the 3D printed holder, slide into the window ducting.
7. Unroll tubing, tape onto a flat piece of wood.
8. Run a blow dryer slowly over the tubing, heating it up.
9. Wait for the tubing to dry and remove the tape. (The tubing should not be bent)
10. Put the 3D printed cup-to-tube attachment over the top cup and insert one end of the tubing. Hot glue the tubing to the attachment for added security.
11. Insert the funnel into the other end of the tubing.
12. Put the 3D printed funnel-to-tubing attachment onto the bottom cup.
13. Fill the bowl with water and add a couple drops of green food coloring.
14. Rest the phone above the window ducting on the cabinet to view down into the top cup.

Here is a shortened procedure to make it simpler and easier to understand. In the images you can see the second step and the fourth step.

1. Measure .0254m (1 inch) from bottom opening, move top cup and opening there.
2. Fill the pitcher with 355ml (1.5 cups) of water and pour into the top cup.
3. Start recording on the phone.
4. Slide the funnel out, hold it in one hand and hold pipette with the other.
5. Squeeze the pipette and release, put the funnel back quickly. (Water flow starts)
6. Once water stops, end recording. Import video into an editing app and record time of flow to three significant figures.
7. Repeat steps 1-6 twice more (3 trials)
8. Repeat steps 1-7 four more times, replacing the 1 inch height in the first step with 3, 5, 7, and 9, inches (heights)

In the images you can see the whole process of simplifying the data and the final data graphed. My raw data was in seconds, which I then averaged out. I divided the amount of water I had in meters cubed by seconds to get the flow rate. I divided that by the cross-sectional area — the area of the opening of the tube — which was in meters squared to cancel out and leave me with meters over seconds, or speed. When graphed it shows little deviation from a linear trend line.

• The greater the difference between the two openings, the greater the speed.
• There is a linear relationship.
• In agreement with Bernoulli Principle.
• When calculated with Bernoulli's Principle, the results are 2-3 times too low.
• Could be due to friction or non-steady flow (not used in the equation), or experimental errors.

• Linear relationship, a greater height difference leads to a greater speed.
• Trend in accordance with Bernouilli’s principle and modern siphon theory.
• Not as many different heights or trials as needed for conclusive results.
• Experimental errors and forces unaccounted for led to deviation from predicted results.
• In the future, different diameter hoses, different amounts of water, different height differences, could be used and contrasted with predicted results to see if the ratio between the predicted and gotten results are the same, or if the deviation was due to unpredictable experimental errors.

As you can see, Bernoulli’s principle was shown to work in speed testing of siphons. However, this experiment was on a small scale and by no means conclusive of whether or not the Bernoulli principle is being used. In the future, I would do this on a larger scale and try to investigate why I got such large deviation from calculated results using the formula.

After the experiment I condensed my data and created a poster board which you can see in the image. In the middle, the shape of a siphon is shown, along with the setup. The image in the center section is of how a siphon can be used to regulate water level in a lake, which I found helpful for understanding how a siphon can be applied in the real world at a larger scale. I presented the data to my class and whole school at a science fair event, and I was chosen to become a Broadcom MASTERS National Science Fair Nominee. Overall I am happy with the results of the project and would like to continue this type of research in the future.