#$&*
course Phy 232
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?
****
The water stream will continue to travel shorter and shorter as the water level in the bottle decreases. At first, the water stream will flow far out from the bottle; however as the water level in the bottle decreases, the distance it travels will shorten. This is because there is less water remaining in the bottle to push the water out of the bottle at a far distance. This distance continues to shrink until just drops are left.
#$&*
Will the speed of the escaping water increase, decrease, or sometimes increase and sometimes decrease? Explain your thinking.
****
The speed of the escaping water will remain constant throughout the process because the size of the straw or tube hole remains the same diameter. Therefore, as long as there is a little bit of water taking up that full diameter and there is a steady stream of water, the flow rate will remain the same. This changes however when the water isn’t steady at the end and just forms droplets.
#$&*
Clearly the water level will decrease. Will it decrease more and more quickly, more and more slowly, or sometimes more quickly and sometimes more slowly? Explain your thinking.
****
The water level will decrease more slowly as time goes on. This is because as the water level is full and it starts to flow out, it has the full amount of water pushing down making the water flow out of the tube. As time goes on, the water level decreases and therefore there is less water in the bottle to push downward. This less amount of water then takes a longer time to decrease. The lower the water level, the slower it takes to continue to decrease.
#$&*
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 interval at the very end will take the longest. This is because there won’t be much water left to push the remaining water out of the bottle, causing it to take more time to finish decreasing the water level all the way. The shortest interval will be from the water being full to the first top interval. This is because there is the full amount of water and the full amount of water weight pushing down on the remaining water causing it to flow out faster than once most of the water drains out of the bottle.
#$&*
List the predicated intervals in order, from the longest to the shortest, and explain your thinking:
****
Longest: Bottom line to reaching the hole because the last bit of water doesn’t have any more water pushing on it to flow out.
Next Longest: Second line to third line because only a little bit more water is present to push the remaining water out.
Third Longest: First line to second line because again there is more water present to push the remaining water out of the tube.
Shortest: Top of bottle to first line because all of the water is present to apply the most weight and force to the water underneath it to force it all out of the tube at a faster rate.
#$&*
Did you predict the order of the four intervals correctly?
****
Yes, my predictions of the four intervals are correct.
#$&*
Now run your first trial. (You will also run a second trial, in which the short piece of thinner tubing is inserted into the larger piece to narrow the flow).
Report your data, and explain what it means. If you used the TIMER include a copy of the display of times (you can just copy and paste the display into a document).
****
1 19.17969 .8359375
2 22.58594 3.40625
3 26.29688 3.710938
4 32.63281 6.335938
#$&*
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).
****
1 143.4766 1.390625
2 148.4688 4.992188
3 153.5234 5.054688
4 158.6172 5.09375
#$&*
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.
"
&#This looks good. Let me know if you have any questions. &#