======Pythagoras Cup======


<WRAP right box>
**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
\\
**Categories:** {{$demo.categories}}
\\


**Alternative titles:** Tantalus Cup, Greedy Cup
</WRAP>

====Summary====                   
{{$demo.summary}}



====Procedure====
Pythagoras cups are commercially available.  The following shows how to build one with everyday materials. 
  - Cut the end of a bendy straw at a 45-degree angle, then trim off the sharp tip.  
  - Bend the straw and insert the short end through a hole in the bottom of a plastic cup, with the bendy part inside.  
  - Hot glue the straw in place inside the cup to prevent leaks.  
  - Seal around the straw on the outside bottom of the cup with more glue.  
  - Place this cup on top of a second cup or a lid so water can drain out of the straw.  
  - Slowly fill the top cup with water.  
  - Observe that the cup behaves normally if filled below the straw bend, but when filled above the straw bend, all the water drains out through the siphon.



====Links==== 
How To Make A Pythagoras Cup Kids Science - TheDadLab: 
{{youtube>SdRdEZcawSc?}}\\

Pythagoras Cup (Greedy Cup) filled with Mercury - Periodic Videos: 
{{youtube>ISfIT3B4y6E?}}\\

📄 Pythagoras Cup - KiwiCo: [[https://www.kiwico.com/diy/stem/motion-mechanics/pythagoras-cup?srsltid=AfmBOoqtv6-4E9-9v0pEidQc66DsmkRhqrdLRDCY-B99f6bP3FXy0obi]]\\

📄 Pythagoras Cup - Tastes of History: [[https://www.tastesofhistory.co.uk/post/pythagoras-cup]]\\


====Variations====
  * Add food coloring to make the siphon effect easier to see.   
  * Experiment with different straw lengths to change the “trigger level” at which the cup empties.



====Safety Precautions====
  * Use caution with hot glue guns—adult supervision required.  
  * Avoid overfilling the cup on surfaces that could be damaged by spills.  
  * Make sure the straw is glued securely to prevent leaks.  
  * Do not drink from the trick cup if glue or non-food-safe materials are used.




====Questions to Consider====
  * Why does the siphon only begin draining once the water rises above the bend of the straw?  
  * What force keeps water moving through the siphon even after the level drops below the bend?  
  * How does this relate to modern siphons used in plumbing or fuel systems?  
  * Why might Pythagoras have used this invention as a lesson in moderation?  
  * What happens if the straw is too short or too long compared to the cup height?