Concepts

Pressure, dynamic pressure, friction

Overview

Water flow through a horizontal tube creates a pressure gradient due to friction. Several vertical tubes sticking out of the horizontal tube show pressure at various points. The effect of dynamic pressure can also be seen by comparing pressures of flowing and stationary water.

Details

Equipment

• [1] Tube network on a mount
• [1] Reservoir beaker with two openings on the bottom
• [1] Receiving beaker
• [1] Rubber stopper
• [1] Lab jack
• [1] Container of red water
• [1] Roll of paper towels

Classroom Assembly

1. Place the tube network on a table.
2. Make sure the reservoir beaker with openings has one of them stoppered and the other joined to entry tube on the tube network.
3. Make sure the exit tube on the tube network is clamped high.
4. Put the lab jack under the reservoir beaker.
5. Elevate the reservoir beaker so that the bottom of the beaker is just below the horizontal tube.
6. Start filling the reservoir beaker with openings, careful not to let air bubbles into the horizontal tube. Fill the reservoir to about 2/3 full.
7. Place the receiving beaker near the exit tube.

Important Notes

• Do not let air bubbles into the horizontal tube. The most frequent cause is by lowering the reservoir beaker below the horizontal tube. If bubbles get in, it can take considerable time and effort to get them out of all the tubes, horizontal and vertical. Air bubbles in the vertical tubes can interfere with pressure measurements.

Script

1. Raise and lower the reservoir beaker to show how the static pressure changes the water level in the vertical tubes.
2. Unclamp the exit tube from the backing plastic and clamp shut the tube.
   
3. Lower the exit tube to the receiving beaker and unclamp the tube slightly. Water should start to flow, decreasing the pressure.
4. Unclamp the tube even more, decreasing the pressure even more.

Additional Resources