LESSON TWO
2
How Are Water Pressure and
Water Flow Related?
Overview
In this activity, students apply the scientific method as they attempt
to answer the question, “How are water pressure and water flow
related?” A large plastic soda bottle, representing a reservoir, is
punched with holes at specific vertical locations. The holes are
plugged with removable stoppers (push-pins) and the bottle filled
LESSON TWO
with water. Students predict which hole, when unplugged, will spray
water farther and why. Students apply the scientific method as they
consider specific questions, make predictions, and observe and
record the results of their experiment. Through their observations,
students gain an understanding of the relationships between water
2
pressure, head, and water flow.
How Are Water Pressure and Water Flow Related?
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LOW IMPACT HYDROELECTRIC POWER
MODULE FOR GRADES 6 TO 8
LESSON TWO
2
Core
Concepts
A hydropower (hydroelectric power)
plant uses the energy of motion in flowing water to rotate a turbine which activates a generator to produce electricity.
An electrical generator is a device that
converts mechanical energy into electrical energy by moving a wire through a
magnetic field. Electricity and magnetism are two aspects of a single electromagnetic force. Magnetism produces
electricity: Whenever an electrical conductor (such as a copper wire) is moved
through a magnetic field, an electric current is produced.
We work
best
under pressure!
The amount of electricity that can be
generated by a hydropower plant is
dependent on the flow rate (the quantity
of water flow in a given time) and the
head (the height from which the water
falls and the pressure behind that water).
These concepts are from the Powering Our
Future Energy Education Conceptual
Framework (Appendix A).
How Are Water Pressure and Water Flow Related?
LOW IMPACT HYDROELECTRIC POWER
MODULE FOR GRADES 6 TO 8
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LESSON TWO
2
Learning
Objectives
ARIZONA DEPARTMENT OF EDUCATION
ACADEMIC STANDARDS
See Appendix B for the full text of these
ADE Standards.
SC06-S1C2-01; SC06-S1C2-03;
SC06-S1C2-05; SC06-S1C3-01;
SC06-S1C3-02; SC06-S1C4-02;
SC06-S1C4-03; SC06-S1C4-05;
SC06-S5C3-01; SC07-S1C2-01;
SC07-S1C2-03; SC07-S1C2-05;
SC07-S1C3-01; SC07-S1C3-02;
SC07-S1C3-04; SC07-S1C3-05;
SC07-S1C4-03; SC07-S1C4-05;
SC08-S1C2-01; SC08-S1C2-03;
SC08-S1C2-05; SC08-S1C3-01;
SC08-S1C3-02; SC08-S1C3-05;
SC08-S1C4-01; SC08-S1C4-03;
SC08-S1C4-05
Science
Mathematics
M06-S2C1-02; M06-S2C1-03;
M06-S2C1-04; M06-S2C1-05;
M06-S2C1-06; M07-S1C2-01;
M07-S2C1-04; M07-S2C1-05;
M07-S2C1-06; M07-S2C1-07;
M08-S2C1-08
After completing this lesson, students
will be able to do the following:
Apply the scientific method by making and
testing predictions.
Analyze data on water pressure and
water flow.
Express results of an experiment
through a graph.
Explain how water pressure influences
water flow.
Describe how flowing water may be used
to do work.
Define and describe the difference
between potential and kinetic energy.
TIME NEEDED
As demonstration — 45 minutes
As student experiment — 90 minutes
TEACHER BACKGROUND
INFORMATION
Review these sections of the Energy Primer:
Renewable Energy Sources
subsection on Hydropower
Also review Parts One and Two of the
presentation, Introduction to
Hydroelectric Power.
How Are Water Pressure and Water Flow Related?
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LOW IMPACT HYDROELECTRIC POWER
MODULE FOR GRADES 6 TO 8
LESSON TWO
Advance
Preparation
2
MATERIALS
Student Data Sheet: Working
Under Pressure — photocopy one
per student
Overhead Transparency: Flowing
Water at Work
overhead projector
calculators
For each student group conducting the experiment, the following equipment is required:
a two liter soda bottle
four push pins
ruler (foot long) or meter stick
water source (such as pitchers, gallon
jugs, or soda bottles full of water)
large tray or plastic sheet (to collect
water if done indoors)
old towels or rags (for spills)
GENERAL PREP
Prepare and test a sample experimental set-up with the suggested materials
so that you are comfortable with the
experiment. Have the example set-up
ready to use in class.
Decide whether students will conduct
the experiment in pairs, teams, or view
it as a teacher demonstration.
(Note: It is recommended that each
student or pair of students get the
opportunity to prepare and test their
own experimental set-up. However, the
activity may be conducted by larger student teams, or by the teacher as a
large-scale demonstration with the
entire class participating and observing.
Your choice may depend on your teaching style, your students’ ability to stay on
task while working in teams, class time,
or to a lesser extent, availability of
materials.)
How Are Water Pressure and Water Flow Related?
LOW IMPACT HYDROELECTRIC POWER
MODULE FOR GRADES 6 TO 8
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LESSON TWO
2
Suggested
Procedure
1
Display the overhead transparency Flowing Water at Work as you introduce this activity. Review the terms potential energy, kinetic energy,
flow rate, and head from the overhead transparency. Ask students to
recall the introductory presentation in which they learned that the
amount of electricity that can be generated by a hydropower plant is dependent
on the flow rate (the quantity of water flow in a given time) and the head
(the height from which the water falls).
2
Explain that it is important for them to recognize that head is more
than just the height from which water is falling. Head is a function of
the height from which water falls, and the pressure behind that
water. (On the transparency, the water behind the dam is exerting
pressure which influences the head of this system.) In this activity, the
class will be conducting experiments which demonstrate how head,
water pressure and water flow are related. These factors relate to how
much work can be done with the water or how much electricity can
be generated at a hydropower plant.
3
Other items to point out on the overhead include:
the location of the turbine in relation to the top of the dam
the measurement of head (the distance from the water surface to
the turbine)
how electricity is generated (The turbine spins the shaft that
goes into the generator and the shaft rotates a magnet inside
coils of copper wire to generate electricity.)
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LOW IMPACT HYDROELECTRIC POWER
MODULE FOR GRADES 6 TO 8
LESSON TWO
2
PROCEDURE CONTINUED
4
Using the sample bottle you created previously, review the experimental set-up. Depending on how you choose to conduct the
experiments (as a demonstration or in student teams), adjust
your introductory explanation to allow for maximum student
inquiry. Regardless of how the experiments will be conducted,
point out the following to students before commencing the activity:
The two liter soda bottle is considered your reservoir. A line
near the very top should be drawn and labeled “fill line.”
You will be attempting to answer the questions: “Will water that
is falling from higher spray out farther?” “Why or why not?”
To answer this question, holes should be punched in the reservoir at four different heights. Explain that the “hole height” is
the distance from the ground (or tray) to the hole. Ask: Where
should those holes be placed to best test your prediction?
Push pins should remain in the holes throughout the experiment and only be removed for the trial with that hole. (Duct
tape may be used to cover the holes if leakage is a problem.)
Three trials should be conducted for each hole and the average distance that the water sprays should be calculated. Why?
Each trial should be conducted by removing the push pin,
noting the distance of the stream of water, replacing the push
pin, and recording the data. The three trials for a specific
hole should be conducted before moving to another hole.
The water in the reservoir should be refilled to the fill line
for each trial. Why?
A standardized system for noting and measuring the distance of water flow for each trial should be predetermined.
Who will observe where the water stream landed and how
will it be measured?
Unless the experiment is conducted outside, a tray or plastic sheet should be placed under and in front of the reservoirs. Whatever is used, it should not hinder the ability to
accurately measure the distance of the water stream.
How Are Water Pressure and Water Flow Related?
LOW IMPACT HYDROELECTRIC POWER
MODULE FOR GRADES 6 TO 8
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LESSON TWO
2
Suggested
Procedure
(continued)
Ask
5
Review the concepts of potential and kinetic energy both in general
and in the context of this experiment: With the sample bottle, point
out that the water behind a particular hole (the water that is about to
be released) has gravitational or potential energy. That is, it has energy that is not yet being used. Water that is flowing out of the hole is
moving and has motion or kinetic energy.
6
Remind students that head is not only the height from which water
falls, but the pressure behind the water. Head is actually a measure of
the system’s potential energy. Point to a hole on the bottle and explain
that the hole height is the distance from the ground (or tray) to the
hole. However, the head of the system would actually be a measure
from the hole to the fill line.
7
8
Pass out the student data sheet Working Under Pressure to each student.
It may be helpful to review the data sheet to ensure students understand the information they should be recording.
Before conducting the trials, students should write their predictions
on their data sheets. You may want to review the scientific method
and describe how this experiment follows the scientific method by
asking them to make and test hypotheses. This might be a good time
to remind them that power production is directly proportional to
the head and the flow of a hydropower system. How might this concept relate to their experiment?
9
10
Have students begin their experiments, guiding them in the initial
data collection if necessary. Remind students to refill their bottles
to the fill line after every trial.
After all of the trials have been completed at all of the hole
heights, students should calculate the averages for each trial and
graph their results. Have students analyze their graphs and complete their data sheets. Note, you may also choose to analyze
the graphs as a class.
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LOW IMPACT HYDROELECTRIC POWER
MODULE FOR GRADES 6 TO 8
LESSON TWO
2
11
Once students have completed their data sheets, conduct a wrap-up discussion with the class using the Discussion Questions from their data
sheets as a guide. Note: Students may be confused as to why water
falling from the higher holes did not spray out the farthest; that head is
a function of both the height of falling water and the pressure behind that water
as applied by the water itself .* Head is a measure of the potential energy
of the system at a given point. In this experiment, the height of the hole
is not the same as the head. Instead, head is more accurately measured as
the distance from the fill line to the hole. (You might refer back to the overhead transparency Flowing Water at Work and point out the measurement
of head as the distance from the water surface to the turbine.) Thus, the
holes nearer to the bottom of the bottle (the ones with more pressure on them from
the water above) would have the greater head (and the greater potential energy).
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(Optional) To further help you orally assess students’ grasp of the concepts, ask them to respond to the following questions (which could be
written on the board):
How are water pressure and water flow related?
How are water pressure and head related?
When does water have kinetic energy? When does water have potential energy?
*Note:
Head, in its most accurate sense, is too complex a concept to adequately explain in this setting to middle school students. In this lesson,
the source of the pressure is only addressed as being a function of the
height of the water and the pressure behind that water as applied by the
water itself.
How Are Water Pressure and Water Flow Related?
LOW IMPACT HYDROELECTRIC POWER
MODULE FOR GRADES 6 TO 8
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LESSON TWO
2
ASSESSMENT IDEAS
Ask students to write down answers to the points in the last step of the
Suggested Procedure. In conjunction with their completed student data
sheets, this should serve as an adequate assessment of their understanding.
EXTENSION IDEAS
Alternate designs: Have students come up with their own experimental designs
to test the concepts of water pressure and flow. Allow them to bring in and use
other materials. See who can come up with a design to have water spray out
the farthest.
Maximizing head: Have students consider the following: How might the water
pressure in the bottle be increased and what might happen to the stream of
water as a result? Create an experiment to test this.
How Are Water Pressure and Water Flow Related?
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LOW IMPACT HYDROELECTRIC POWER
MODULE FOR GRADES 6 TO 8