How can a fountain run with no pump?

Students assemble and prime a three-bottle Hero's fountain, then investigate why water falling into a sealed bottle can push water up out of a nozzle with no pump. They test how the drop from the basin to the floor bottle controls the fountain and use energy reasoning to show it is not a perpetual-motion machine.

Anchor phenomenon

How can pouring one cup of water into a bowl make a fountain shoot up out of the middle of it, with nothing plugged in?

Learning objectives

Students will be able to explain how falling water compresses trapped air and how that air pressure pushes water out of the nozzle.
Students will be able to trace the path of water and the path of air through the fountain on a labeled diagram.
Students will be able to predict and test how raising or lowering the floor bottle changes the fountain's height.
Students will be able to use the idea of gravitational potential energy to explain why the fountain eventually stops.

Lesson flow (5E)

Engage8 min

Day 1. Set up the demonstration fountain with the floor bottle on the floor, and ask students to predict what will happen when you pour a cup of water into the basin. Prime it and let the fountain run. Then lift the floor bottle above the basin so the fountain stops, and set it back down so it starts again. Students write what they noticed and one question.

Explore30 min

Day 1. Groups connect their hoses using the diagram (basin drain to the floor bottle's long tube, floor bottle's short tube to the supply bottle's short tube, supply bottle's long tube to the nozzle), fill the supply bottle about three-quarters full of colored water, set the heights, and prime their fountain. They watch which bottle fills and which empties, and whether the fountain gets shorter as it runs.

Explain7 min

Day 1. Using the projected diagram, lead the class through the cause-and-effect chain: water falls into the sealed floor bottle and takes up space, the trapped air is compressed and its pressure rises, that air is connected to the supply bottle, and the higher pressure pushes the supply water up the long tube and out of the nozzle. Introduce compress, air pressure, prime and potential energy.

Elaborate30 min

Day 2. Groups run a fair test: they change the drop from the basin to the floor bottle (floor bottle on a chair, on the floor, at the bottom of a step) and measure the fountain height with a meter stick, keeping the nozzle, amount of water and supply bottle height the same. Groups that finish early try a narrower nozzle and compare the stream. Each group records results in a table and shares one finding.

Evaluate15 min

Day 2. Students draw the fountain with arrows showing where the water goes and where the air goes, and complete the worksheet for their age group. Close with the question: is this a perpetual-motion machine? Students answer in writing using the words potential energy and where the water ends up.

Discussion questions

What did you notice about which bottle filled up and which bottle emptied while the fountain ran?
Is the empty floor bottle really empty? What is inside it, and what happens to that when water pours in?
Why did the fountain stop when the floor bottle was lifted above the basin?
How did the size of the drop from the basin to the floor bottle affect how high the fountain went?
The fountain lifts water above the basin. Does that mean the water gains energy overall? Where does all the water end up?
Why does the fountain slowly get shorter as it runs, and what would you change to make it run longer or higher?

Common misconceptions

Common ideaHero's fountain could run forever if it had no leaks.What the demonstration showsAll the water ends up in the lowest bottle, so the system loses potential energy overall. It stops when the supply runs out or the water levels reach equilibrium.

Common ideaAn empty bottle has nothing in it.What the demonstration showsThe bottle is full of air. The air takes up space, and when water pours in, that air is squeezed and pushes back.

Common ideaWater cannot be pushed upward without a pump.What the demonstration showsA difference in air pressure can push water upward. Here, the pressure comes from water falling into a sealed bottle.

Common ideaThe water in the nozzle is the same water you just poured into the basin.What the demonstration showsThe poured water drains into the floor bottle. The fountain water comes from the supply bottle, pushed out by compressed air.

Assessment

Exit ticket: "Explain why the fountain stopped when the floor bottle was lifted above the basin."
Labeled diagram: students draw the three bottles and use two colors of arrows to show the path of water and the path of air.
Review the fair-test table on the 11-14 worksheet for a correctly identified changed variable (the drop), measured variable (fountain height) and controlled variables.
Quick performance task: give a group a fountain that is not running and ask them to get it going and explain each step.

Differentiation

Support: Give younger students fully pre-connected fountains so they only fill, set heights and prime. Focus on the 8-10 worksheet items about predicting, watching which bottle fills, and what happens when the floor bottle is lifted. A color-coded hose diagram helps students follow the connections.

Extend: Older students measure the drop and the fountain height for several setups, graph fountain height against drop, and compare their results to the idea that the jet can rise roughly as high above the supply water as the water falls into the floor bottle. They can also research Hero of Alexandria or connect the fountain to water towers and gravity-fed water systems.

Classroom safety. The teacher drills caps (held with pliers or a clamp), cuts bottles and tubing, and handles the hot glue gun before class. Cover cut bottle edges with tape. Water will spill, so work outdoors, near a sink, or over trays and towels, wipe up spills right away so nobody slips, and use extra care if testing near steps. Food coloring can stain clothing.

At a glance

Grades: Grades 4-8
Time: Two 45-minute classes
Grouping: Groups of 3-4

Materials

Per group: 1 pre-built cap set (3 drilled, glued caps with tubes), 2 empty 2-liter bottles plus 1 cut catch basin, 3 pieces of flexible hose, a tall support for the basin, a cup or small pitcher, a meter stick, towels, and a tray or plastic bin to stand in
For the class: water with blue food coloring in a few pitchers or jugs, extra hose and tape for leak repairs, plenty of towels or a mop, and a dropper tip or aluminum foil for narrower nozzles
Teacher demo: one complete working Hero's fountain, plus a clear diagram (drawn or projected) of the three bottles and the tubing layout

Teacher prep

Build one working demonstration fountain first and run it at least once to find leaks (about 45 minutes, plus glue cooling time).
Prepare one cap set per group ahead of time: drill two holes in each of three caps (hold caps with pliers or a clamp), push the rigid tubes through, and seal both sides with hot glue. This is a teacher job; allow about 15-20 minutes per set.
Cut a catch basin for each group from the top third of a 2-liter bottle and tape over the cut edge.
Cut the rigid tubing and flexible hose to length for each kit and bag the pieces with a simple hose-connection diagram.
Plan a wet work area: a hallway near a sink, outdoors, or tables covered with towels or plastic, with a tall support (jar, box or books) at each station and a step or low stool for testing bigger drops.

Standards (NGSS)

5-PS1-1 Develop a model to describe that matter is made of particles too small to be seen.
MS-PS3-2 Develop a model to describe that when the arrangement of objects interacting at a distance changes, different amounts of potential energy are stored in the system.
3-5-ETS1-2 Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.

Practices: Developing and Using Models, Planning and Carrying Out Investigations, Constructing Explanations
Crosscutting: Cause and Effect, Energy and Matter, Systems and System Models