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Earth Science


Lesson Title: How does a siphon work?

By Collette Craig

Overview: A siphon is a tube or pipe system used to move a liquid from one container to another container that is at a lower level and over a point between the two that is higher than either container.

Grade level: 6-9

Educational Standards: From the Nevada State Science Standards: 1.8.1, 1.8.2, 20.8.1, 20.8.2.  From the National Science Education Standards: Contents Standards A and B.

Lesson Overview:  This lesson is designed for middle school students.  The goal is to develop a student's understanding of how a siphon works.  The lesson includes a hands-on activity, a computer illustration and explantion of a siphon, as well as some historical information about the Virginia City inverted siphon.

Time requirement: This lesson is designed for a time period of 90 minutes.


Materials: Two 250 beakers, 50 cm of tubing rubber or plastic (available at most hardware stores), and 150 ml water for each group.

Procedure: Work in groups of 2-3 students. Print out copy of the student activity and give one copy to each group. Students will complete the activity as described in the student page. In their journals, students will make observations and answer the questions on the page plus any generated by the student.

Teacher backround:  What is happening?  When both legs of the siphon are full, because of gravity, the hydrostatic force (the force of the water) is greater on the higher side of the tube. This means the liquid will move up the lower leg of the tube, over the rim of the beaker and into the lower beaker. Once started, the flow will continue until the water levels are equal, then the forces on each leg of the tube will also be equal.

Siphons range in size from the simple glass, metal, or rubber instruments used in chemistry laboratories to aqueduct piping systems used to transmit liquids over an elevation or hill. Large siphoning units, such as are used in municipal water-supply systems, frequently have an air-removal valve at the top to eliminate the presence of air at the highest point, which would block the liquid flow.

Assessment: Assessment is embedded in the student responses in the journals.