Your 'flow experiment' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** Your initial message (if any): **
** Is flow rate increasing, decreasing, etc.? **
Rate of flow is very fast at first and begins to decrease as more and more fluid leaves the cylinder
** Is the velocity of the water surface increasing, decreasing, etc.? **
The velocity of the water surface and buoy would decrease as the rate of water leaving the cylinder decreases.
** How would the velocity of the water surface, the velocity of the exiting water, the diameter of the cylinder and the diameter of the hole be interrelated? **
Velocity of the water surface and the exiting water are directly proportional. As the velocity of the water exiting decreases, the velocity of the water surface decreases.
The larger the diameter of the cylinder, the slower the velocity of the water surface, but it should not affect the velocity of exiting water.
The larger the diameter of the hole, the faster the velocities of the water surface and exiting water.
** Explain how we know that a change in velocity implies the action of a force: **
The change in velocity is due to the gravitational force or pressure exerted on the water inside the cylinder. This force pushes the water down and out of the hole. This pressure decreases as the amount of water in the cylinder decreases and therefore, the velocity of water exiting the cylinder decreases.
** Does the depth seem to be changing at a regular rate, at a faster and faster rate, or at a slower and slower rate **
From the pictures above, the depth seems to be decreasing at an increasing rate, but in fact the depth should decrease at a decreasing rate because of less pressure. The pictures may not have been taken at equal time intervals.
** What do you think a graph of depth vs. time would look like? **
A graph of depth vs time would show the depth decreasing at a decreasing rate. (Concave up)
** Does the horizontal distance (the distance to the right, ignoring the up and down distance) traveled by the stream increase or decrease as time goes on? **
The horizontal distance decreases over time because the pressure pushing the water out is decreasing. Therefore, the water would not be forced out, but instead begin run more vertically down.
** Does this distance change at an increasing, decreasing or steady rate? **
The distance decreases at an increasing rate.
** What do you think a graph of this horizontal distance vs. time would look like? **
A graph of horizontal distance vs time would show the horizontal distance over time decreasing at an increasing rate (Concave down).
** The contents of TIMER program as you submitted them: **
Note: Both of my pieces of ¼ tubing were sealed, so I had to use a piece of the 1/8 tubing at the bottom of my cylinder. The tubing was not big enough and therefore, the water leaked out the sides. I tried to prevent this by wrapping a cottonball around it.
0
1.671875
1.90625
2
2.375
2.571875
2.671875
2.84375
3.65625
4.765625
5.515625
9.921875
** The vertical positions of the large marks as you reported them, relative to the center of the outflow hole **
0.5 cm
2.1
3.7
5.2
6.8
8.3
9.8
11.3
12.8
14.2
15.7
17.1
** Your table for depth (in cm) vs clock time (in seconds) **
0 sec, 17.1 cm
1.671875, 15.7
1.90625, 14.2
2, 12.8
2.375, 11.3
2.571875, 9.8
2.671875, 8.3
2.84375, 6.8
3.65625, 5.2
4.765625, 3.7
5.515625, 2.1
9.921875, 0.5
&#It appears you have reported time intervals rather than clock times. A time interval is the time between two subsequent clicks; a clock time is the running time from the beginning of the experiment. For example if a series of events occurs at clock times t = 2, 5, 9 and 18 seconds, then the time intervals between these events are 3, 4 and 9 seconds. If the time intervals between a series of four events were 7, 5 and 4 seconds, then if the clock started with the first event the clock times would be 0, 7, 12 and 16 seconds. Be sure you understand the difference between clock time and time interval.
&#
I believe that the entire time elapsed during your experiment was probably around 35 seconds, not 9.9 seconds. So your last clock time should have been 30-some seconds.
** Is the depth changing at a regular rate, at a faster and faster rate, or at a slower and slower rate? **
My graph shows that the depth is decreasing at a decreasing rate. The graph begins a steep decrease and continues to decrease but flattens out near the end.
** Your description of your depth vs. t graph: **
I believe that I thoroughly described the graph in the previous question. My graph shows that the depth is decreasing at a decreasing rate over the time intervals. It is concave up and looks like half of a U.
** Your explanation and list of average average velocities: **
I obtained my velocities by subtracting the distance the water surface moved over each interval and divided it by the time. In other words, I divided the change in distance by the change in time.
.8374 cm/s
.7869
.7
.6316
.5832
.5614
.5275
.4376
.3147
.2901
.1613
You did this correctly and your results make good sense.
However you should have reported clock times rather that time intervals. Had you done so then your calculation would have corresponded to dividing the change in the second-column quantity by the change in the first column quantity rather than dividing the difference between the second-column quantities by the number in the first column.
** The midpoints of your time intervals and how you obtained them: **
I found the midpoints of the time intervals simply by adding consecutive time intervals together and dividing them by two.
.83594 sec
1.7891
1.9531
2.1875
2.4734
2.6219
2.7578
3.25
4.2109
5.1406
7.7187
Your procedure is correct, but to get the midpoint of a time interval you must perform this operations on clock times rather than on time intervals.
** Your table of average velocity of water surface vs. clock time: **
0.83594, 0.8374
1.7891, 0.7869
1.9531, 0.7
2.1875, 0.6316
2.4734, 0.5832
2.6219, 0.5614
2.7578, 0.5275
3.25, 0.4376
4.2109, 0.3147
5.1406, 0.2901
7.7187, 0.1613
** Your description of your graph of average velocity vs clock time: **
This graph looks very similar to the other graphs. It shows that the average velocity of the water surface is decreasing at a decreasing rate over average time intervals. (Concave up)
** Your explanation of how acceleration values were obtained: **
To find the acceleration of the water surface I divided the change in consecutive velocities by the time interval (difference in times) between them. From the negative acceleration values, we can conclude that the water surface velocity is slowing down.
-.0529 cm/s^2
-.5299
-.2918
-.1693
-.1468
-.2494
-.1826
-.1279
-.0265
-.0499
** Your acceleration vs clock time table: **
0.95316 sec, -.0529 cm/s^2
0.164, -.5299
0.2344, -.2918
0.2859, -.1693
0.1485, -.1468
0.1359, -.2494
0.4922, -.1826
0.9609, -.1279
0.9297, -.0265
2.5781, -.0499
Your accelerations should have been based on differences in clock times; it seems that they were based rather on differences in time intervals.
** According to the evidence here, is acceleration increasing, decreasing, staying the same or is in not possible to tell? **
This data indicates that the acceleration of the water surface is decreasing overall. This is to be expected since my original hypothesis was that the water surface was decreasing at a decreasing rate. The acceleration should be decreasing. There is some variation between data points because acceleration does not consistently decrease.
You did a good job with most of this experiment, but I think your reported clock times were in fact time intervals. I think your velocities are probably calculated correctly, but I don't think this is the case with your accelerations. I could be wrong, so see my notes and let me know what you think.