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course PHY 232
2/18 16:37
Brief Flow Experiment________________________________________
Use a plastic soft-drink bottle and the TIMER program, as well as two short open tubes from the Initial Materials package (sent for free when you submitted your address, according to the email request made previously). If you don't yet have those materials you can improvise with a drinking straw and a plastic soft-drink bottle.
The experiment just asks fora few predictions and some data, and once set up takes only a few minutes to run. Don't go to a lot of trouble trying to be overly precise, but do try to be reasonably accurate (e.g., +- a second on timing, +- a few millimeters on positions of the three lines, +- a centimeter or two on the horizontal range of the stream). You'll be refining things and taking a little more care on followup trials. You should easily be able to get this done before Monday.
Do spend some time on the problems and submit what you are able to get prior to Monday's class. You'll learn a lot more in class if you do so. We'll be going over the questions in class.
You are going to do the following (don't do it yet; predict first what will happen):
• Punch a hole the side of the bottle, near the bottom.
• Insert a piece of tubing into the hole to direct the flow of water from the bottle.
• Fill the bottle with water.
• Set it on a tabletop or on the counter next to the sink (or on the ledge of a bathtup, etc.--any setup will do as long as the bottle rests on a level surface, and the escaping stream has at least 15 cm to fall before it hits something).
• Let the water run out, with the stream falling freely to the surface below.
What do you expect will happen? Answer the following:
Will the water stream tend to travel longer and longer distances before striking the surface below, shorter and shorter distances, or will the distance tend to increase at times and decrease at times? Why do you think the distance traveled by the stream will behave as you say?
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The water will travel shorter and shorter distances (horizontally) over time because as water escapes the bottle the remaining water at the level of the hole is under less and less pressure.
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Will the speed of the escaping water increase, decrease, or sometimes increase and sometimes decrease? Explain your thinking.
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The speed will also decrease for the same reasons, the pressure inside the bottle is reduced over time.
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Clearly the water level will decrease. Will it decrease more and more quickly, more and more slowly, or sometimes more quickly and sometimes more slowly? Explain your thinking.
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More and more slowly - the change in height is also related to the pressure which is decreasing. (As well as the density and gravity which do not)
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Now set up and prepare to take some measurements:
Punch or cut a hole about 1/8 inch (.3 cm) in diameter in the side of the bottle, at a point where the side of the bottle is vertical, within a few centimeters of the bottom of the bottle. If you cut the hole, a triangle about 1/8 inch on a side is about right.
Your initial materials will include short open pieces of tubing, one whose diameter is the same as that of the 'cap' on the bottlecap and tube, the other having the same diameter as the tube. Insert the larger of these pieces into the hole. The piece should fit fairly tightly in the hole, so when the bottle is filled much more of the water that flows from the bottle will flow through the tube rather than around it. You can test this by filling the bottle, placing your thumb over the end of the tube, and seeing how much water leaks out. Then move your thumb and verify that the water flows out much more rapidly.
Mark three points on the bottle, one at the top of the cylindrical section of the bottle, one halfway between the first mark and the hole, and one halfway between the second mark and the hole. Measure the three distances, relative the the hole, with reasonable accuracy.
You will set the bottle it a vertical position and release your thumb. You will time the fall of the water level, reporting the clock times at which the water reaches the first mark, and each subsequent mark.
You will report the vertical positions of the three lines, relative to the hole, and the observed clock times. Your data will be used to determine the duration of each of three intervals:
• During the first interval the water level falls from the highest mark to the second-highest.
• During the second interval the water level falls from the second mark to the third.
• During the third interval the water level falls from the third mark to level of the hole. The water will be considered to have reached the level of the hole when it starts falling from the bottle in separate drops rather than a stream or a continuous series of drops.
Before you actually perform the experiment make some additional predictions:
Which of the four intervals will last the longest, and which will be the shortest?
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List the predicated intervals in order, from the longest to the shortest, and explain your thinking:
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Third, First, Second
I am assuming the ones with the greatest change in height will take the longest.
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Did you predict the order of the four intervals correctly?
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I went ahead and ran the first trial so that I could answer this question. Yes, the projection was correct although the first and second interval were relatively close.
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Now run your first trial. (You will also run a second trial, in which the short piece of thinner tubing is inserted into the larger piece to narrow the flow).
Report your data, and explain what it means. If you used the TIMER include a copy of the display of times (you can just copy and paste the display into a document).
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1 105.6152 105.6152
2 109.8438 4.228516
3 113.0313 3.1875
4 119.7715 6.740234
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Determine, as accurately as you can using a clock or watch with a second hand, the clock times at which the water reaches the first mark, the second, the third and the clock time at which the flow from the hole reduces to the point where it leaves the hole in distinct drops.
Run your second trial, in which the short piece of thinner tubing is inserted into the larger piece to narrow the flow.
Report your data, and explain what it means. If you used the TIMER include a copy of the display of times (you can just copy and paste the display into a document).
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1 84.32422 84.32422
2 93.43359 9.109375
3 100.7578 7.324219
4 112.7969 12.03906
It appears to take longer because the smaller tube restricts the amount of water that can flow out.
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Determine, as accurately as you can using a clock or watch with a second hand, the clock times at which the water reaches the first mark, the second, the third and the clock time at which the flow from the hole reduces to the point where it leaves the hole in distinct drops.
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end document
&#Very good responses. Let me know if you have questions. &#