Hands-on Activity: Too Much Pressure! Modeling Force-Pressure-Area Relationships

Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

A photograph shows a hand directing a high-pressure stream of water from a hose onto an asphalt road surface. It's a Honda GX160 5.5 HP. pressure washer in action.
Students learn about water pressure.
copyright
Copyright © 2007 Mark Schellhase, Wikimedia Commons CC BY-SA 1.2+ https://commons.wikimedia.org/wiki/File:Pressure_Wash.JPG

Summary

Students learn all about water pressure and how engineers design faucets. Teams build simple systems that model faucets and test them to see the relationships between pressure, area and force. This is a great outdoor activity on a warm day and gives students experience in experimentation, design and teamwork. A student worksheet is provided for guidance and data collection.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

Engineers exploit the relationships between, pressure, force, area and work when designing different mechanical and fluid systems. Fluid systems may include the piping system in and throughout a single building or a whole city water system. The design of pumps and valves for the piping system include pressure and work calculations. Another example that uses the concepts of fluid and mechanical systems is the heating and ventilation system in a building—a damper in an air duct acts like a valve in a piping system, but for air instead of water.

Pre-Req Knowledge

Some knowledge about diameter and area to complete Part 3 of this activity, measurement.

Learning Objectives

After this activity, students should be able to:

  • Explain how water pressure changes with height.
  • Describe how the area of an opening affects the force of water flow.
  • Design and evaluate a model faucet.

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Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Know the formulas for the area and circumference of a circle and use them to solve problems; give an informal derivation of the relationship between the circumference and area of a circle. (Grade 7) Details... View more aligned curriculum... Do you agree with this alignment?
  • Knowledge gained from other fields of study has a direct effect on the development of technological products and systems. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Materials List

Each group needs:

  • 2-3 empty plastic 10-16 oz bottles
  • 2-3 2-foot sections of plastic tubing of varying diameters
  • 3 feet of duct tape
  • 1 bucket or catch basin
  • 1 gallon of water
  • corks or rubber stoppers
  • scissors
  • Too Much Pressure Worksheet

Introduction/Motivation

Have you ever played outside with a garden hose on a warm day? What happens to the flow of water when you bend the hose in half? (Answer: The water stops flowing.) What happens when you put your finger over the end of the hose? (Answer: The water sprays or the water flow stops.) Sometimes you can get the water in the hose to come out in a small stream, but then this stream comes out faster and the water shoots farther across the yard. Why is that? It happens because the smaller opening increases the velocity (speed) and pressure of the water coming out of the hose.

What happens when you swim in the deep end of a pool? What happens as you go deeper and deeper in the pool? Your ears may begin to hurt. In fact, your ears hurt because of the pressure of the water. How do you think water pressure and depth is related? (Have students discuss the answer with the person sitting next to them and then discuss their answers as a class.) The deeper you go the more pressure there is and the more your ears hurt. The same thing is true for air pressure (another fluid) and height. The higher in the air you go, the more pressure you feel in your ears.

These things are determined by the properties of fluid flow (in these examples, air and water). Fluid flow and fluid properties are concepts that engineers need to know about when designing a many things, including the water plumbing for our houses, buildings and schools, etc. Engineers need to think about how water is going to get through pipes, and ultimately to our sinks. They need to think about how to get enough pressure for the water to flow through the pipes and the faucets, so we can wash our hands or get a drink of water.

Today we are going to experiment with some of the properties of fluid flow. We are going to play with water, do some measurements, and think like an engineer to use what we learned in designing a faucet.

Procedure

Background

The measurement portion of this activity is modeled after the following equation:

Q = V*A

where Q = flow (ft3/min or gallons/minute), V = Velocity (ft/min), and A = Area (ft2)

For example, as your thumb decreases the area across the tube (kind of like closing a valve at the end of the tube), per the equation above, a decrease in area results in a higher velocity, assuming the flow stays the same. It is similar to putting your thumb over the end of a garden hose to get it to spray further. Assuming the flow is constant, a decrease in area results in a higher velocity of the fluid so that it shoots further out, or puts more pressure on your thumb.

Before the Activity

  • A week prior to the activity, ask students to bring in empty/rinsed plastic soda bottles to accumulate a supply for the activity.
  • Gather materials and assemble supplies for each group.
  • Make copies of the Too Much Pressure Worksheet, one per group.
  • Cut off the bottom ends of the bottles. Alternatively, include this task for students to do in step 1 of the Assembly.

With the Students

Introduction and Design Challenge

  1. Present to the class the Introduction/Motivation content to kick off the project.
  2. Organize the class into groups of two students each.
  3. Distribute supplies and a worksheet to each group.
  4. Make sure students understand that today they are going to work as if they are engineers who are trying to figure out the best design for a faucet.

Part 1: Assembly

Have students assemble the pressure testing device as follows, which is also provided as assembly instructions on the worksheet.

A drawing shows an upside down bottle with tubing inserted into the opening of the bottle showing the assembly needed for the device. The variable "height" is defined as the vertical distance from the water line to the bottom opening of the tubing.
Firgure 1: Device assembly.
copyright
Copyright © 2006 Chris Sheridan, ITL Program, College of Engineering, University of Colorado Boulder

  • Insert the plastic tubing about one inch into the top of a bottle (as shown in Figure 1).
  • Wrap duct tape around the tube and bottle top in order to form a watertight seal, as shown in Figure 2.

A photograph shows three different test bottle setups with varying diameter tubes.
Figure 2: Three duct-taped test bottles.
copyright
Copyright © 2006 Malinda Schaefer Zarske, ITL Program, College of Engineering and Applied Science, University of Colorado Boulder

  • Have one student hold her thumb securely over the end of the tube.
  • While holding the device over a catch basin, have a second student fill the bottle about ¾  full with water.
  • Still over the catch basin, hold the bottle 2 feet above the end of the tube (where you thumb is stopping the water at the end of the tube), as illustrated in Figure 3.

A photograph shows a cola bottle held upside down over a sink with clear plastic tubing attached with duct tape to the bottle neck. The bottle is filled with water.
Figure 3: Final experimental setup.
copyright
Copyright © 2006 Malinda Schaefer Zarske, ITL Program, College of Engineering and Applied Science, University of Colorado Boulder

Part 2: Experiment

  • Have teams follow the steps of the experiment as outlined on the worksheet.
  • Have students answer the corresponding worksheet questions.

Part 3: Measurement

  • Have students measure the diameter and area of the tubes in their experiment and record their measurements on the worksheet. Note: The worksheet requires students to calculate the area of each tube. If time is limited, skip this step by the teacher providing the area of each tube.
  • Have students repeat the steps of the experiment with the next two different bottles.

Part 4: Engineering Design

  • Have students think about their experiment and measurement. How can they use what they learned to design a faucet?
  • Permit students to use available supplies such as corks, stoppers, tape, and anything else, to make the final part of their faucets, which will ultimately control the water flow.
  • Have them draw their designs on their worksheets.

Attachments

Safety Issues

Remind students to be careful with the water and not let it splash anywhere but into the catch basin.

Troubleshooting Tips

In order to see a difference in the force for different areas, water pressure must be kept the same. This is maintained by making sure to hold up the plastic bottles such that the top water line is always at approximately the same height.

Assessment

Pre-activity Assessment

Prediction: Ask students to predict the following answers (relationships):

  • How are pressure and height related?
  • How are area and pressure related?

Activity Embedded Assessment

Worksheet: Have students record measurements and follow along with the activity on the Too Much Pressure Worksheet. After the worksheets are completed, have students compare answers with their peers. Review the worksheet answers to gauge their mastery of the subject.

Post Activity Assessment

Worksheet Discussion: Review and discuss the worksheet answers with the entire class. Use the answers to gauge students' mastery of the subject.

Prediction Analysis: Have students compare their initial predictions with their test results, as recorded on the worksheets. Ask the students to explain how pressure, area and height are related.

Show and Tell: Have the students "show and tell" to the rest of the class the faucet designs they created, explaining their work to the other students.

Activity Extensions

As a class, generate a list of a few characteristics of water on the board or someplace where everyone can see them. Then, ask the students to think of a common item that an engineer designed with that fluid property in mind. Examples of fluid characteristics might include that water flow increases with height or depth, water force increases with smaller opening, that water has to be held together in a container, etc.

Have the students think about the pressure in a water column. How much pressure is there at the deepest point in the ocean, the Mariana trench? First, find the depth of the trench and use the hydrostatic pressure gradient equation to calculate the pressure ( ). Research the answer at http://www.marianatrench.com/

Activity Scaling

For younger students, eliminate the area calcuation and provide more specific instructions.

Contributors

Chris Sheridan; Jackie Sullivan; Malinda Schaefer Zarske; Janet Yowell; Melissa Straten

Copyright

© 2006 by Regents of the University of Colorado

Supporting Program

Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

Acknowledgements

The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation (GK-12 grant no. 0338326). However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.

Last modified: March 17, 2018

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