#$&*
Phy 202
Your 'measuring atmospheric pressure' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** Measuring Atmospheric Pressure_labelMessages **
Indicate below how the system behaves (what changes when you do what, how the system's reactions to your actions appear to be related to one another) and how it 'feels'.
----->>>>> behavior
Your answer (start in the next line):
Squeezing the bottle causes the water to rise up the tube. It feels like a small to moderate squeeze will be sufficient to get good results in measurements.
#$&*
Using a measuring device you will measure the relative positions of the meniscus as you vary your squeeze:
• One of the ruler copies used in the previous experiment on the distortion of paper rulers should be used here; a reduced copy should be used for greater precision. You may choose the level of reduction at which you think you will achieve the greatest level of precision. Only relative measurements will be important here; it will not be necessary to convert your units to actual millimeters or centimeters.
Indicate below the level of reduction you have chosen, and your reasons for this choice.
----->>>>> level of reduction and reasons
Your answer (start in the next line):
I am using the reduction of 2cm:1real cm. This allows for a greater precision in measurement, yet still legible to read.
#$&*
In the units of the measuring device you have chosen, write down in your lab notebook the readings you used to indicate length of the air column, from the meniscus to the barrier at the capped end. No conversion of the units of your device to standard units (e.g., millimeters or centimeters) is required. Your information should include the marking at one end of the measuring device, and the marking at the other. If necessary two or more copies of paper rulers may be carefully taped together.
Indicate in the first line below the length of the air column in the units of your measuring device.
In the second line explain how you obtained your result, including the readings at the two ends and how you used those readings to indicate the length.
----->>>>> air column length, how obtained incl readings and how used
Your answer (start in the next line):
50.0cm
I taped two of the rulers together end-to-end and added the measurement at the meniscus to the top of the air column
#$&*
Now place the same measuring device along the tube, positioned so you can observe as accurately as possible the relative positions of the meniscus in the pressure tube.
• It is recommended that the initial position of the meniscus be in the vicinity of the center of the measuring device, so that position changes in both directions can be observed.
• It is not necessary for the measuring device to extend the entire length of the air column, as long as you know the reading on the measuring device that corresponds to the initial position of the meniscus. From this information and from subsequent readings it will be easy to determine the varying lengths of the air column.
• Take whatever precautions are necessary to make sure neither the measuring device nor the pressure tube can move until you have completed the necessary trials.
Mark positions along the vertical tube at 10-cm intervals (actual 10-cm intervals as indicated by a full-sized ruler) above the surface of the water in the bottle.
• If the bottle is pretty full, as described before, it might be possible to make the first mark on the vertical tube at 10 or 15 cm above the water surface.
• Marks may be made using an actual marker, or pieces of tape, or anything else that happens to be convenient.
Write your information in your lab notebook:
• Write down the position of the first mark on the vertical tube with respect to the water surface (e.g., 10 cm or 15 cm).
• Write down the position of the meniscus in the pressure tube. This position will simply be the reading on your measuring device. For example if the meniscus is at marking 17.35, that is what you write down.
• As in all labs, you directly record what you read. Never do any arithmetic between making an observation and recording it.
You will now conduct 5 trials, raising water to the first mark on your vertical tube and reading the position of the meniscus before the squeeze and while water is at the given level.
• Squeeze the bottle until water reaches the first mark in the vertical tube, and carefully read the position of the meniscus in the pressure tube. Release the bottle and immediately write down that position.
• Repeat, being sure to again write down the position of the meniscus before squeezing the bottle (this position might or might not be the same as before) and the position of the meniscus when the water is at the first mark in the vertical tube.
• Repeat three more times, so that you have a total of five trials in which the water was raised to the first mark in the vertical tube. With each repetition you will write down two more numbers.
Record your information below:
• Indicate on the first line the vertical position of the first mark on the vertical tube, relative to the water surface, giving a single number in the first line.
• On the second line give the length of the air column, as measured in units of the device you used to measure it.
• On the third line, give the position of the meniscus before the first squeeze then the position of the meniscus when the water in the vertical tube was at the first mark. Give this information as two numbers, delimited by commas.
• On lines four through seven, give the same information for the second through the fifth trials.
• Starting in the eighth line give a brief synopsis of the meaning of the information you have given and how you obtained it.
----->>>>> vert pos mark vert tube, air column lgth, meniscus pos 1st trial, same 2d, same 3d, same 4th, same 5th trial, meaning
Your answer (start in the next line):
15.00
17.05
17.10, 18.05
17.10, 18.10
17.05, 18.15
17.00, 18.05
17.05, 18.05
These are the measurements of the meniscus in the tube before and after the squeeze, for 5 trials. The results show that in order to raise the water in the vertical tube by 15cm, the height of the water in the pressure measuring tube increased by about 1cm.
#$&*
Now repeat the 5-trial process, this time raising water to the second mark. Write down everything as before.
In the space below report your results, using the same format as before:
----->>>>> same for 2d vert pos
Your answer (start in the next line):
25.00
17.05
17.10, 19.05
17.05, 19.10
17.05, 18.95
17.10, 19.00
17.05, 19.05
These are the measurements of the meniscus in the tube before and after the squeeze, for 5 trials. The results show that in order to raise the water in the vertical tube by 25cm, the height of the water in the pressure measuring tube increased by about 2cm.
#$&*
Repeat again, raising water to the highest mark you can manage with normal effort. Remember that this isn't supposed to be a test of strength.
In the space below report your results, using the same format as before:
----->>>>> same for 3d pos
Your answer (start in the next line):
45.00
17.05
17.05, 20.00
17.05, 19.95
17.10, 20.05
17.10, 20.10
17.05, 19.90
These are the measurements of the meniscus in the tube before and after the squeeze, for 5 trials. The results show that in order to raise the water in the vertical tube by 45cm, the height of the water in the pressure measuring tube increased by about 3cm.
#$&*
If the highest mark you can easily manage is the third mark, then you may stop. If you have raised the water to a mark higher than the third, then do one more series of 5 trials, this time choosing a mark about halfway between the second and the highest mark.
In the space below report your results, using the same format as before. If you were not able to raise the water higher than your third mark, simply leave these lines empty.
Then report the approximate percent change in the length of the water column for each of the three vertical heights. Report in a single line separated by commas, and in the last line indicate how you got these results, including a sample calculation for the second set of trials.
----->>>>> same for 4th pos if possible
Your answer (start in the next line):
35.00
17.05
17.10, 19.45
17.05, 19.50
17.05, 19.55
17.05, 19.50
17.05, 19.55
These are the measurements of the meniscus in the tube before and after the squeeze, for 5 trials. The results show that in order to raise the water in the vertical tube by 35cm, the height of the water in the pressure measuring tube increased by about 2.5cm
#$&*
Make your estimate of atmospheric pressure:
• What was the maximum height to which the water column was raised?
• How much pressure was required to support the column?
• Based on the behavior of the air column in the pressure tube, what percent do you think this is of atmospheric pressure?
• What therefore do you conclude is atmospheric pressure?
----->>>>> max ht, pressure to support column, percent of atm pressure, conclusion atm pressure
Your answer (start in the next line):
The maximum height the water column was 45.00cm. The pressure of about 20.00cm of water was needed to support the column. Knowing that atmospheric pressure is based on the pressure of air above a measurement point, I would estimate that this is about 95% of atmospheric pressure. This would make atmospheric pressure about 100 kPa
#$&*
Your instructor is trying to gauge the typical time spent by students on these experiments. Please answer the following question as accurately as you can, understanding that your answer will be used only for the stated purpose and has no bearing on your grades:
• Approximately how long did it take you to complete this experiment?
3 hours
** Measuring Atmospheric Pressure_labelMessages **
&#Very good data and responses. Let me know if you have questions. &#