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Background: For this experiment we used “Speed of a Bubble” tubes. These are long glass tubes filled with a fluid of unknown viscosity with an air bubble in it. Viscosity, informally known as thickness of a fluid, means the resistance a fluid has when flowing. The bubble in the tube is displaced when the tube is flipped over, because the fluid, which is more dense, in the tube slides down, causing the less dense bubble to get pushed up to the top. Also, since the bubble is filled with a gas, it rises, whilst the fluid, which is a liquid, is pulled down by gravity. We used this tube to test whether the angle at which the tube is tilted would affect the velocity at which the bubble traveled up the tube.If one were to ask what the real life application of this lab was, it would be air embolism.
Air embolism is a condition that happens when there are bubbles of air/gas present in ones vein or artery, blocking the blood from flowing through (as seen in the diagram on the previous page). It can occur when you are exposed to high pressure, causing air to be allowed to travel through your vein or artery . This is related to our experiment, because it also deals with a fluid with a viscosity (blood), in a tube (ones vein/artery), that has an air bubble floating through it. Once the tube becomes too small and the friction increases, the bubble in the tube (vein/artery) gets stuck and blocks it. Also, since the viscosity of blood is quite high, it is already harder for the bubble to flow through. On top of that, since the bubble is floating up (due to it being a gas), it could in some part of your body be going against the flow of the blood, producing even more friction. Doctors use this knowledge and sometimes have patients sit down to slow down/stop the embolism from going to the patients lungs, heart, and brains (2). It is like changing the angle of the tube (veins/arteries) to slow down/stop the bubble from going. So, in the end, this experiment can be related to a real life example of air embolism.This experiment can teach us a lot about how the bubble moves and the angle at which to slow it down to help/stop the embolism from flowing further up to important body parts such as the brain.
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- 1 Timer (accurate to the hundredths)
- 1 Wooden meter stick (with millimeters)
- 1 Protractor (make sure the 0/180° mark can touch the surface of the table when you measure the angle, or else you can’t measure the angle correctly)
- 1 Masking tape
- 1 Ring stand
- 1 Blue “Speed of a Bubble” tube (filled with a fluid of which we do not know the viscosity)
- 1 Metal Screw Clamp
1. Set up the lab as seen in the diagram
2. Use the protractor to measure your first angle measurement (20°). Adjust the clamp on the ring stand so that when the tube leans on it, the angle at which the tube is tilted at the degrees you are measuring (20° in this case).
3. Have one partner flip the tube so that the bubble is at the bottom of the tube and put the tube in place (the end of the tube against the tape on the table and top on the clamp). Have the other partner press “start” on the timer once the front of the bubble passes the 0.4 m tape mark on the tube (as labeled on the diagram) and stop the timer once the bubble reaches the end and has stopped moving.
4. Record the time measured in a data table.
5. Repeat steps 3-4 three times to get three sets of data for that angle.
6. Repeat steps 2-5 but for your second angle measurement (30°).
7. Repeat steps 2-5 for your third angle measurement (45°).
8. Repeat steps 2-5 for your fourth angle measurement (60°).
9. Repeat steps 2-5 for your fifth angle measurement (90°).
9.1.Once you have collected three sets of data (and uncertainties) for all your angle measurements, find the average time and the average uncertainty (the range of your three trials from that angle measurement divided by two).
9.2.Find the velocity of the bubble for each angle measurement by dividing the distance traveled (0.4 meters) by the average time you calculated for the angle measurement.
Based on the data we collected, we can answer our research question “What is the effect of changing the angle at which the ‘Speed of a Bubble’ tube is tilted on the velocity of the bubble going up the tube” by saying, “that the velocity increases till around 60° and then decreases again”. This causes the graph to look like a parabola where the “a” value of the standard form quadratic equation (ax^2 + bx + c = 0) is negative. We can use our data to confirm this answer. To prove this right, the angles, 20° and 90° should have the lowest velocity, since they have a 40° and 30° difference. If we look at the data, we see that the average time for the angle of 20° (5.56 +/- 0.07) and that for the angle of 90° (5.72 +/- 0.03) are the highest values. The angle of 60°, however, has the fastest average time of 4.64 +/- 0.05. If we are then to calculate the velocity of those points, which can be calculated by dividing the distance (0.04 m) by the average time you got for that angle, then we would get a velocity of 0.07 m/sec for the angle of 20°, 0.07 m/sec for the angle of 90°, and 0.09 m/sec for the angle of 60°. The other angles we measured that are in-between 20°-60° increase in velocity (they are more than the velocity of the angle of 20°, but lower than that of the angle of 60°) and the ones in-between 60°-90° decrease in velocity (they are lower than the velocity of the angle of 60°, but higher than that of the angle of 90°). This means that the data is in the shape of a parabola, since it increases then decreases. The “sweet-spot” seems to be around 60°, because the velocity is the highest for that angle. These results make sense, because there should be a “sweet-spot” and increasing/ decreasing velocities. It the slope is too steep, then the bubble is trying to float up quickly and the fluid is being pulled down by gravity quickly, causing the fluid to slide down on both sides of the tube. This produces a great amount of friction, since the bubble is being pressed in between the liquid. This then causes the velocity to decrease. However, if the slope is too gradual, then the fluid is not being pulled straight down by gravity and the bubble is floating up slowly. Instead the fluid is being pulled against the glass tube, increasing the friction with the glass, on top of the friction with the bubble. So, if there is a right balance in the slope of the tube, then the gravity will pull the fluid down in a way that produces the least friction with the bubble, and the bubble will have the right angle to float up against the glass to the top of the tube with the least friction. With our data we can see that the balanced spot, the “sweetspot”, is around 60°. The intercept of the line of best fit at (0,0.05), however does not fit the
experiment. At an angle measurement of 0°, the velocity should be zero, causing the intercept to be at the origin (0,0). Since this is not the case, and it intercepts at (0,0.05), we can conclude that this is due to the errors that occurred during this experiment. If one were to continue this experiment for further investigation, then I would expect the graph not to continue decreasing until the x-axis, but to curve back up and increase. This would cause it to look like a sine graph that starts at the y-axis does not cross the x-axis. I would expect this, because once one has done the angles between 0° and 90°, then the angles between 90° and 180° are just the same slope, but in a different direction. This would produce similar results as it’s corresponding angle (the angle with the same slope) in the other quarter (0°-90°). On a graph this would look like a repeated wave (sine graph), on which each corresponding curve is very similar.
During this experiment, my lab partner and I were aware of multiple errors that occurred and could have had an effect on the results we got.
Firstly, it there was error in timing the bubble, because it was difficult to catch the bubble passing the “starting line” and pressing start on the timer at the same time. This was because the bubble would pass under the tape and the person timing then had to react very quickly to start the timer once it saw the beginning of the bubble come from under the tube. There was a slight timing error there, causing the time to run either a bit more or a bit less that it actually should. Also, the timing for the stopping wasn’t easy either, since the bubble had to stop move at the top. However, sometimes it stopped moving, so the timer would press stop, but actually it still had to bounce back and come to a halt. These timing errors would affect the velocity we measured.
Secondly, our protector was printed on a thin piece of plastic that was very bendable. This made it hard to measure the angle accurately, because if it was slightly bended, it would affect the degrees at which we tilted the tube. In return, this error in angle would affect the time it took for the bubble to reach the tube, causing the velocity for that angle to not be exactly what it should be. It could have been the velocity for an angle 1°-2° higher or lower, just because the protractor was not easy to use.
Finally, since time was essential in this lab and we had to be very quick to flip the tube and place it where it needed to be, there were certain times where the tube’s end was not exactly where it needed to be (on the piece of tape on the table). When we failed to do so, the angle at which the tube was tilted would be affected. Again, this means we would record the velocity for an angle 1°-2° higher or lower, which affected the average velocity we calculated for the angle we were originally trying to measure.
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- B. Braun Melsungen. Air Embolism. Digital image. Causes of Air Embolism. Safe
Infusion Therapy, 2016. Web. 13 Sept. 2016. <http://www.safeinfusiontherapy.com/images/
- Elert, Glenn. “Viscosity.” Physics Info. The Physics Hypertextbook, 2016. Web. 13 Sept.