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Activity: The Effects of Pressure

NGSS Disciplinary Core Ideas:

Materials

  • Table 9.2
  • Two 50 mL graduated syringes
  • 5 cm length of tubing
  • Water in a bowl
  • Safety glasses
  • Towels

Procedure

Safety Note: Be sure to use care when handling contents under pressure. Wear safety glasses to protect eyes from pressurized water.

 

In this activity, the syringe barrels simulate a free diver’s rigid skeletal structure. Air and water in the syringes simulate the gases and liquids in the diver’s body. By pressing the plungers of the syringes, we can test whether increased pressure causes the air and the water to compress, or decrease in volume. By pulling the plungers, we can test whether decreased pressure causes the air and the water to expand, or increase in volume.

 

<p><strong>Fig. 9.12.</strong> Testing how pressure changes affect the volume of (<strong>A</strong>) air, (<strong>B</strong>) water, and (<strong>C</strong>) an air-water system.</p><br />


 

A. Investigate the effect of increased pressure on air volume.

  1. Assemble the equipment as shown in Fig. 9.12 A.
    1. Fill each syringe with 30 mL of air.
    2. Connect the syringes with tubing.
       
  2. Predict what will happen to the volume of the air in the syringes when pressure is increased.
    1. Review Fig. 9.12 A
    2. Record your predictions in Table 9.2.
       
  3. Test the effect of increased pressure on gas volume by pushing in on the plungers of both syringes. Be sure to use equal force on both plungers. Observe the volume of the air when it is under increased pressure. Record your data in Table 9.2.
     
  4. Release the pressure on the plungers. Observe and record what happens to the volume of air in each syringe.
     
  5. Disconnect the tubing before continuing to Procedure B.

 

B. Investigate the effect of decreased pressure on air volume.

  1. Predict what will happen to the volume of the air in the syringes when pressure is decreased. Record your predictions in Table 9.2.
     
  2. Reassemble the equipment so that each syringe is filled with 30 mL of air. Record the starting volume of the air.
     
  3. Test the effect of decreased pressure on air volume by slowly and steadily pulling both plungers. Observe what happens to the volume of the air. Record your data in Table 9.2.
     
  4. Release the plungers. Observe what happens. Record your data.
     
  5. Disconnect the tubing before going on to the next procedure.

 

C. Investigate the effects of changing pressure on water.

  1. Repeat Procedures 1 and 2, this time using 30 mL water in each syringe. Fill the syringe with water by pushing the plunger all the way down until it stops, so that no air remains in the chamber. Place the end of the syringe in the bowl of water and pull up on the plunger until it fills to 30 mL. Eliminate any air bubble in the syringe by pointing the open end up and tapping on the side of the syringe. Expel the air by pushing lightly on the plunger. Be sure that the tubing contains water and connect the two syringes to the tubing (see Fig. 9.12 B).
     
  2. Record your predictions and observations in Table 9.2.

 

D. Investigate the effects of changing pressure on a mixed air-water system.

  1. Repeat Procedures 1 and 2, this time filling one syringe to 30 mL with water and the other to 30 mL with air (see Fig. 9.12 C). Connect the two syringes with tubing that is half-filled with water.
     
  2. Record your predictions and observations in Table 9.2.

 

Activity Questions: 
  1. How did you measure the volume of the air and the water in the syringe system?
     
  2. When pressure increased, what happened to the volume of the air? What happened to the volume of the water?
     
  3. When pressure decreased, which showed the greater increase in volume: air or water? Hypothesize an explanation for your answer.
     
  4. How did an increase in pressure affect the air-water system? How did a decrease in pressure affect it?
     
  5. Did any air or water leak from the system when you moved the plungers? Did any air or water enter the system? How could you demonstrate your answer?
     
  6. Did the mass of the air or water change when you pushed on or released the plungers? How do you know?
     
  7. Apply what you have learned from the syringe system to the effects of pressure on the human body.
    1. Which do you think is more affected by changes in water pressure: the air in the lungs of a free diver or the liquids in their blood and body tissues? Explain your answer.
    2. What do you think happens to the volume of a free diver’s body when descending? What do you think happens to the lungs, the blood, other tissues, and the skeletal structure?
    3. What happens to a free diver’s body when they ascend?
       
  8. If you had to transport supplies in a submarine or a spaceship—vessels with limited space—how would you transport air? Water?
     
  9. What would have happened if you did not use the same amount of force on the two plungers in procedure A, step 3? What if you only pushed down on one plunger?
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.