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course PHY 202
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 have to travel shorter and shorter distances because as it runs out there will be less pressure pushing it out of the bottle.
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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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I think the speed of the water might increase and decrease in spurts, because that’s what happens when you try to dump out a bottle upside down. The water will come out in bursts and the air bubbles in the bottle rise to the top in bursts.
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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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I think that the water level will decrease sometimes more quickly and sometimes more slowly, in bursts, as with the speed of the escaping water.
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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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The 1st interval will be the shortest, and the 3rd interval will be the longest.
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List the predicated intervals in order, from the longest to the shortest, and explain your thinking:
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The intervals lengths will be backwards, with the third interval being longest, the second interval being shorter, and the first interval being even shorter, because at the beginning (first interval) the pressure is the highest causing the water to exit faster.
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Did you predict the order of the four intervals correctly?
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NOPE! I definitely wasn’t thinking about how the distances were different, even though I knew it would slow down at the bottom.
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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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This was done using an online stopwatch timer, not the TIMER program.
Interval 1 = 9.5 cm 20 seconds
Interval 2 = 5 cm 19 seconds
Interval 3 = 5cm 29 seconds
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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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Interval 1 = 9.5 cm - 27 seconds
Interval 2 = 5 cm - 24 seconds
Interval 3 = 5cm - 36 seconds
Trial 2 worked out the same way, with the second interval being shortest. The experiment was the same, only the overall process was longer because the flow had been narrowed.
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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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&#Your work on this lab exercise looks good. Let me know if you have any questions. &#