DIY: Pythagoras Cup | Tinkerer Box Blog

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Pythagoras Cup

Stem Activities

Ages: 9-12

Less than 30 minutes

Grownup needed

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Explore an ancient and ingenious invention - the Pythagoras Cup, also known as the 'Cup of Justice' or 'Greedy Cup'. This fascinating device from ancient Greece is not just a work of art but reveals our ancestors' profound understanding of liquid measurement and balance.

Materials Needed

Plastic bottle
Cup of water
Tape
Rubber band
Plastic cup
Food colouring
Plasticine
Stirring stick
Pencil
Scissors
Straw
Ruler
Tray

An assortment of materials arranged on a light wood-grain table appears ready for a science experiment or craft project. A white rectangular tray holds two clear glass containers, one partially filled with water, a roll of orange tape, a small bottle of blue liquid, a lump of blue putty or clay, a wooden craft stick, a pencil, and a pair of scissors. A clear plastic water bottle lies beside the tray, and an orange drinking straw and a clear plastic ruler are positioned next to the tray. The image suggests preparation for a hands-on activity.

Step-by-step tutorial

Step 1

Using scissors, cut the plastic bottle 7cm from the top.

A hand holds a clear plastic water bottle against a light wood-grain background. A pair of scissors is positioned to cut the bottle near its base. The image suggests the bottle is being repurposed or modified for a craft project or experiment.

Step 2

Place plasticine under the bottle cap and use a pencil to make a hole in the centre of the cap large enough for the straw.

Two hands manipulate a white plastic bottle cap sealed with light blue putty or clay on a light wood-grain surface. One hand holds the cap and putty base while the other hand uses a pencil to poke a hole in the center of the cap. This suggests a craft or science activity involving repurposing everyday materials.

Step 3

Bend the straw and cut the longer end to 12cm length.

Two hands are shown on a light wood-grain background interacting with an orange drinking straw. One hand holds a shorter, bent section of the straw, while the other hand uses scissors to cut a longer, straight piece. A black line indicating 12cm spans the length of the longer straw segment, suggesting measurement and preparation for a craft or science activity.

Step 4

Take the rubber band and bind the straw sides together as shown. Be careful not to bind too tightly, as liquid needs to flow through.

Two hands hold a flexible orange drinking straw against a light wood-grain background. The straw has been bent into a loop at the top and a small orange rubber band secures the base of the loop to the longer, straight portion of the straw. The hands appear to be adjusting or tightening the rubber band. The image suggests a craft project or the construction of a simple toy or tool.

Step 5

Use scissors to make a small hole in the bottom of the plastic cup.

A hand holds the bottom portion of a clear plastic bottle against a light wood-grain background. Scissors are being used to make a small cut or notch in the center of the bottle's base. This implies the bottle is being prepared for a craft project or science experiment that requires modification.

Step 6

Screw on the cap with the hole and place plasticine underneath it.

Two hands hold the top portion of a clear plastic bottle, including its white cap, against a light wood-grain background. A ball of turquoise putty or clay is affixed to the bottle cap. The image suggests the creation of a homemade device or toy using repurposed materials.

Step 7

Thread the longer end of the bound straw through the small hole in the plastic cup.

Two hands hold a clear plastic cup and an orange drinking straw against a light wood-grain background. A section of flexible orange straw, bent and secured with a small orange rubber band, is inserted into the cup. One end of the straight straw protrudes from the cup while the bent section remains inside, suggesting the construction of a simple pump, toy, or science experiment.

Step 8

Continue threading the straw through the plasticine and bottle cap.

Two hands hold a clear plastic bottle and a clear plastic cup connected by an orange straw against a light wood-grain background. A ball of turquoise putty or clay is wrapped around the bottle's opening and the straw, creating an airtight seal. The flexible portion of the straw is inside the cup, and the setup resembles a homemade pump or air pressure experiment.

Step 9

Position the plastic bottle opening upwards and use the pencil end to seal around the straw-cap connection with plasticine, ensuring it's completely airtight.

A hand holds the top, cut-off portion of a clear plastic bottle against a light wood-grain background. A white bottle cap, sealed with turquoise putty or clay, is visible inside the larger opening of the bottle. A gray pencil or similar cylindrical object is being inserted through the putty and into a small orange straw that is embedded within the putty. This suggests a science experiment or craft project involving airflow or pressure.

Step 10

Add food colouring to the water and stir thoroughly.

A hand holds a small bottle of blue dye or ink over a clear glass of water, set on a light wood-grain background. Drops of the blue liquid are being dispensed into the water, creating swirling patterns and demonstrating the diffusion or mixing of liquids.

Step 11

Place your completed Pythagoras Cup on the tray.

A homemade contraption constructed from a clear plastic bottle and cup, connected by an orange straw, sits on a white tray against a plain white background. The bottle is inverted and attached to the cup, which is upright. A small amount of turquoise putty or clay is visible around the bottle's opening where it connects to the straw. The setup suggests a science experiment or DIY project, possibly related to air pressure or water flow.

Step 12

Now, pour the coloured water into the cup. What happens?

A hand pours bright blue liquid from a clear beaker into a clear plastic cup positioned on top of an inverted clear plastic bottle on a white tray. The bottle and cup are connected by an orange straw sealed with turquoise putty. The blue liquid is partially filling the cup, and the setup suggests a science experiment demonstrating air pressure, siphoning, or fluid dynamics. The background is plain white.

The Science Behind It:

The Pythagoras Cup, allegedly invented by the Greek mathematician Pythagoras, is specially designed to allow normal use when filled with an appropriate amount of liquid. However, if overfilled, the siphon mechanism at the bottom activates, causing all the liquid to drain away - symbolising how greed leads to losing everything.

The cup works using the siphon principle: when liquid exceeds a certain threshold, the internal pipe system triggers the drainage of all liquid, creating an interesting physical phenomenon.

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