Science STEM Project for Kids: How to make a siphon 'Pythagoras Cup' at home with cups

Introduction

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In today's post, we will be making something cool, as usual. Have you ever hosted a party and then you are worried about some people taking more portions of drinks than others? Worry no more, as we will make a special cup, known as the Pythagoras cup to prevent that from happening. We will also use this opportunity to learn how Siphon works.

This is a very cool STEM project for middle school kids!!

Getting excited already? Continue reading to learn more about this cup.

Pythagoras Cup

A Pythagorean cup (also known as a Pythagoras cup, Greedy Cup, or Cup of Justice) is a practical joke device in the form of a drinking cup, credited to Pythagoras of Samos. This cup was invented to spot greedy people when being asked to take their portion of a drink.

A Pythagorean cup looks just like a regular drinking cup, except that the bowl has a central column in it. The central column of the bowl is positioned directly over the stem of the cup and over a hole at the bottom of the stem. (basic explanation of the column is a bent straw passed through a hole at the bottom of a cup).

When a liquid is poured into the cup, pressure also pushes the water to go up the shorter end of the straw. Once the cup is filled beyond the height of the straw, a siphoning effect causes the cup to drain its entire contents through the hole in the base.

Pythagoras cup (Wikipedia)

Now, let us replicate the Pythagoras cup using household items around us and get ready to give justice to the greedy LoL!!

Materials Needed

3 Transparent plastic cups
A pair Scissors
Bendy plastic straw
Glue
Bowl of colored liquid (this can be regular water mixed with food coloring)
Used/old Compact disc (optional)

Materials needed

Setting up our Pythagoras cup

Step 1

Pick the first cup and make a hole at the bottom center using scissors. (the hole should just be big enough for your straw to fit through, so as to prevent leakage)

Make a hole in the cup with scissors.

Step 2

If your straw is not bent all the way down, you can tape the short end of the straw to the body and then push the longer end of the straw through the hole made in the cup.

Secure the short end of your straw to the body with tape.

Push your staw through the hole in the cup.

Step 3

Secure the straw to the hole with glue and make sure the hole is waterproof (to avoid unwanted leakage). Our Pythagoras cup is now ready.

Secure the straw to the cup with glue to avoid leakage.

Step 4

Pick your second plastic cup and place the compact dist above it then place your Pythagoras cup on top of the disc with the straw passing through the center of the disc into the cup below. (This setup helps balance the cup when you are pouring the liquid into the Pythagoras cup)

Step 5

Pour some water into the third cup and add some coloring to make the liquid visible enough. (you can use food coloring to add color to your water)

Third cup filled with colored liquid.

Testing and Workings

Pour your colored liquid into the Pythagoras cup.

As can be seen below: the water stays intact in the Pythagoras cup as it hasn't gone above the straw height.

As soon as the liquid rises above the straw, the pressure makes the water that entered through the shorter end of the straw inside the cup to then cross over into the longer side of the straw and then drain down.

The water keeps draining until the Pythagoras cup is empty.

Real-world application - Siphon Toilet

Most modern flush toilets operate on the Siphon principle (let me explain):

Siphon toilet workings (Reynolds plumbing)

Water enters the Tank through the Inlet tube.
The Float ball prevents water from rising above the height of the Siphon and causing the Pythagoras cup effect (automatic flushing). That is where the Piston comes in.
With the handle, you can then raise the water level to go above the piston when needed which will then cause the siphon to flush the toilet.

Other cute things to make and hand-crafts for kids

If you are looking for more ideas for STEM projects to do with your kids, take a look at these other activities:

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