Pressure in Liquids
In this experiment, you will see a U-tube manometer to measure the pressure exerted by solids and by liquids. The U-tube manometer measures the pressure in terms of the difference in liquid level in the arms of the tube.
Use water in your manometer for this activity.
Objectives:
1. To describe how pressurein a liquid varies with depth.
2. To calculate the pressure given the depth of liquid
3. To state the factors upon which the pressure exerted by a solid depends
Materials:
- U-tube mounted on wood (each arm is about 22 cm long)
- Small glass funnel
- Thin rubber sheet (5cm by 5cm)
- Tall glass container or beaker about 1000 cu.cm capacity
- Standard masses: 100g, 200g, 300g, 400, 500g
Procedure:
The centimeter(cm), is used here for measuring heights of liquid columns for your convenience. However, you will need to convert cm to meters(m) to enable you to use the SI unit of pressure which is Pa.
1. Stretch the rubber sheet to cover the mouth of the glass funnel and secure it with a string or tape. Then measure the diameter of the rubber sheet on the funnel's mouth.
2. Fill the U-tube arms with colored water up to about 1/3 full from the bottom of the tube using dropper. (take care not to introduce air pockets or bubbles inside the U-tube.) Set a ruler beside each arm of the U-tube and secure the masking tape.
3. Attach one end of the rubber tubing to the spout of the funnel and the other end to the arm of the U-tube. Note that the atmosphere exerts pressure on the water surface in the tube. Attach the rubber sheet to the funnel.
4. Press on the rubber sheet a few times while carefully observing the liquid level in each U-tube arm.
5. Mark the sides of the glass container or beaker in cm using masking tape. Place the zero mark about 1/3 height of the beaker from the mouth.
6. Fill the beaker with colored water up to the zero mark. Then immerse the funnel about 1 cm deep with rubber sheet surface up. Observe and record the levels of the colored water in arms A and B.
7. Continue lowering the funnel to 2cm, 3cm and so on up to the bottom of the beaker. Each time take note of the water levels in arms A and B of the U-tube. Record the height of the water levels in Tables 1.1
Table 1.1 Record and Observation Made
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Depth of Immersion (cm)
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Arm A Level (cm)
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Arm B Level (cm)
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Arm Level Difference (cm)
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Pressure (Pa)
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1
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2
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3
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4
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5
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6
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7
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Diameter of the rubber sheet: __________cm
8. Hold the funnel with its rubber sheet up. Place 100g mass on the rubber sheet. Record the reading of each U-tube arm.
9. Repeat step 8 but use 200g mass instead of 100g; then use 300g, 400g, and 500g masses. Record your results in Table 1.2
Table 1.2 Record of Observations Made
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Mass on Rubber Sheet (g)
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Arm A Level (cm)
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Arm B Level (cm)
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Arm Level Difference (cm)
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Pressure (Pa)
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100
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200
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300
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400
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500
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Questions:
1. With both ends of U-tube open, why are the water levels the same in both arms of the tube?
2. Explain why the water levels are observed to be the same in both arms of the tubes when one arm of the tube is connected to the funnel.
3. What happens to the liquid levels in arms A and B when you press on the rubber sheet of the funnel? Explain.
4. What is the effect of immersing the rubber sheet into the beaker of water?What does this indicate?
5. Examine the data in table 1.1 Compare the difference in water level to the corresponding depth of immersion of the rubber sheet. Are these two distances related?