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Make a fountain that doesn’t need an electric pump. This fountain was designed by Heron, a Greek teacher and inventor in 1st Century CE.

Safety: This activity involves using an electric drill, a sharp knife and a hot glue gun. Adult help is required.

You will need

• 3 x empty plastic water bottles with lids. Try to pick bottles with nice wide lids.
• 1.5 metres of thin aquarium hose. We used 2.5-millimetre wide hose
• Electric drill
• Drill bit set
• Hot glue gun and glue sticks
• Scissors
• Sharp knife
• Paper clip
• Jug of water
• Towels
• Blu-tack

What to do

1. Take 2 bottle lids and with an adults help, fix them together, back-to-back, using the glue gun. Then carefully glue around the whole edge of the join to prevent any leaks.
2. Select a drill bit, slightly bigger in diameter than the hose. We used a 3-millimetre drill bit.
3. Ask an adult to drill 2 holes side by side, approximately 5mm apart, in the double bottle lid we made.
4. Ask an adult to drill 2 holes side by side, approximately 5mm apart, in the remaining single lid.
5. Now using a bigger drill bit, drill a hole through the base of one of the bottles. We used a 10-millimetre drill bit for this step.
6. Glue the back of the single lid over the hole in the bottle you have just made, ensuring that you don’t block the holes in the lid with glue. Then carefully glue all the way around the join to prevent any leaks.
7. With an adults help, use scissors to cut the top half off one of the bottles. You’ll only need the top half of this bottle.
8. Time to put things in order! The whole bottle will be the base of your fountain. On top of this, screw on the double lid.
9. Take the bottle you glued a lid to, turn it upside down and screw it into the other side of the double lid. We’ll call this bottle the ‘middle’.
10. Finally, take the top half of the last bottle and screw it into the lid on the top of the stack. We’ll call this bottle the ‘funnel’.
11. You will need to cut three lengths of hose using the scissors, measure the hose against the bottle set-up. The hose 1 will extend from the bottom of the funnel to the bottom of the base bottle. This is the longest piece of hose.
12. Hose 2 will extend from the top of the lower bottle to the top of the middle bottle.
13. Hose 3 will extend from the bottom of the middle bottle into the funnel. Add another 15 centimetres at the top so you can bend the hose into a spout.
14. Take the bottles apart again and feed the hoses you have just cut through the holes in the lids as shown in the diagram.
15. Now, using the glue gun glue each hose into its place in the lids, ensuring that there will be no leaks.
16. Put the bottle set up back together with all the pipes in place.
17. Feed the paperclip into the top hose in the funnel, and then bend the hose into a spout. Phew, we’re nearly there!
18. Now to prime the fountain. Do this step in a wet area in case you spill water. Slowly pour water into the funnel at the top. If you have connected it correctly this will run down hose 1, filling up the bottom bottle.
19. When the bottom bottle is mostly full, turn the fountain upside down and allow the water to run through hose 2 into the middle bottle. When this is complete turn the fountain right way up again.
20. To start the fountain, pour water into the funnel at the top and watch the flow of water.

Troubleshooting

There’s a lot going on in this activity, and it often doesn’t work the first time you try.

If nothing is working, make sure all your pipes are going between the right bottles. Also make sure you haven’t accidentally blocked one of the pipes!

If something is dripping, or you’re getting a stream of air bubbles, you’ve probably got a leak. Empty the fountain out over a sink, and then try to seal any gaps with blu-tack. The drips and bubbles usually happen near the leak, so try fixing that spot first.

What’s happening?

Heron’s fountain works using water displacement and air pressure.

As water is poured into the funnel, gravity pulls it down hose 1 into the base bottle. The base bottle slowly fills with water and the air inside gets compressed. Some of that air flows up hose 2 into the middle bottle.

As the pressure in the middle bottle increases, the water in this bottle is forced up hose 3 to make a fountain. Then that water falls into the funnel, keeping the fountain going.

This flow of water will continue until either the water rises too high in the bottom bottle or the water level in the middle bottle falls too low. To reset the fountain turn it upside down to refill the middle bottle, empty the water from the bottom bottle and pour it back into the funnel.

Perpetual motion

You might think this fountain could run forever, and that it can make infinite energy. However, it’s not that special.

To power the fountain, water falls from the very top to the very bottom. The water coming up and out the fountain only travels from the middle bottle to the top, which isn’t nearly as far.

If you watch the water levels carefully, you’ll notice that the middle bottle is emptying and the bottom bottle is filling. The water is going downhill, it’s just taking a tricky path to get there.

Any machine that runs forever without needing more energy is called a perpetual motion machine. Perpetual motion is impossible because it breaks the laws of physics. That hasn’t stopped people from trying to make one, but none of them have ever worked. And if physics is right, no perpetual motion machine will ever work.