Session 3: Pressure and Height – Experiment 1

Objectives 1:  Observe that the pressure varies with the height of water.

Explanation:

The hydrostatic pressure of a given fluid is function of the height of the fluid above the considered point. Holes are perforated in a bottle full of liquid, and the jet will be less energetic depending on the height with respect to the water.

Material:

Part A

The simpler version of this activity can be done using 1.5 or 2 -liter soda bottles taped together The more sophisticated version consists of a pipe with one small exit hole drilled near the bottom and seven large holes drilled along it and plugged with rubber stoppers. The separation between the hole centers is 5 cm (can be varied)

Part B

Container with three different-size holes drilled at the same height (the holes should not be too small)

Maximum duration

45 minutes

Main activities

(Ref: http://www.tos.org/hands-on/teaching_phys.html)

Part a

  1. You have a pipe with one small exit hole near the bottom and several large holes plugged with rubber stoppers. You can fix the height of the water column above the exit hole by simultaneously covering the bottom exit hole with your finger and filling the tube until water flows out one of the upper large holes (after removing a stopper from the hole). Make sure you have placed the ruler perpendicular to the bottom of the pipe.
  2. Before you use this apparatus: What do you expect will happen when you fill the tube with water to the height of the first large hole (from the bottom) and release your finger from the exit hole? Explain your expectations in terms of the forces acting on the fluid. What do you expect will happen when the water height above the exit hole is increased? Why?
  3. Test your predictions. Begin by removing the rubber stopper from the lowest large hole. Simultaneously, hold your finger over the small exit hole, and fill the pipe with water until it runs out the hole the stopper was in. (Think: Why do we want to maintain a fixed water level within the tube?) Using a ruler, measure the height of the water column above the exit hole. Then, remove your finger from the exit hole letting the water run out, while you continually fill the pipe with water to maintain the same height of water column above the exit hole. Note how far the water squirts when it first strikes the ruler. Replace the stopper and repeat the steps for the next four holes, working up one hole at a time.
  4. Plot the distance at which the water hit the ruler as a function of the height of the water column for each of the holes. Are the data consistent with your prediction in Step 2?
  5. Would the distance that the water travels, for any given hole, change if the holes were bigger? Why?


Part b

  1. Take the second pipe (or box) (with three holes of different diameters), cover all three holes with your finger(s), and fill the pipe with water. Place the ruler perpendicular to the bottom of the pipe. Uncover one hole at a time and measure the distance at which the water first strikes the ruler. Does your observation agree with your reasoning in Step 5 above (Part A)?

Conclusion/Plenary