#$&*
course Phy 232
5-31-11 about 11:45 p.m.
Brief Flow ExperimentUse 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?
****
Shorter and shorter, because the pressure of the water coming out of the tube will decrease as the water level falls in the bottle
#$&*
Will the speed of the escaping water increase, decrease, or sometimes increase and sometimes decrease? Explain your thinking.
****
Decrease, because the pressure of the water coming out of the tube will decrease as the water level falls in the bottle
#$&*
Clearly the water level will decrease. Will it decrease more and more quickly, more and more slowly, or sometimes more quickly and sometimes more slowly? Explain your thinking.
****
More and more slowly, because the less water in the bottle means that the pressure of the water coming out will decrease which controls how fast the water level decreases.
#$&*
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?
The shortest interval will be the 1st, longest the 3rd interval
#$&*
List the predicated intervals in order, from the longest to the shortest, and explain your thinking:
3rd, 2nd, 1st. Because as the water drains out the pressure decreases, higher pressure will push the water out faster.
#$&*
Did you predict the order of the four intervals correctly?
****
#$&*
Now run your first trial. (You will also run a second trial, in which the short piece of thinner tubing is inserted into the larger piece to narrow the flow).
Report your data, and explain what it means. If you used the TIMER include a copy of the display of times (you can just copy and paste the display into a document).
1 7.359 7.359
2 38.996 31.637
3 59.307 20.311
4 89.022 29.715
The 1st clock time is the initial clock time, 2nd is when the water level reached the 2nd mark from the top, 3rd is when the water level reached the 3rd mark from the top, and the 4th is when the water level reached the hole. The 1st interval time was 31.637sec, the 2nd interval time was 20.311sec, and the 3rd interval time was 29.715sec. In longest to shortest intervals it was 1st, 3rd, 2nd.
#$&*
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).
1 7.468 7.468
2 46.888 39.42
3 78.917 32.029
4 124.353 45.436
The 1st clock time is the initial clock time, 2nd is when the water level reached the 2nd mark from the top, 3rd is when the water level reached the 3rd mark from the top, and the 4th is when the water level reached the hole. From longest interval to shortest is 3rd, 1st, 2nd.
#$&*
@& Your data should indicate depth also. Perhaps it does in a subsequent line.*@
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."
@& Time data look good.
Can you insert your data on the positions of your three marks and resubmit?
&#Please see my notes and, unless my notes indicate that revision is optional, submit a copy of this document with revisions and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes.
If my notes indicate that revision is optional, use your own judgement as to whether a revision will benefit you. &#