Amilk carton filled with water is hanging from a string. what will happen if you punch two holes in opposite sides of the carton at the opposite corners?

When you punch holes in opposite corners of a milk carton filled with water which is hanging from a string, water will start to flow outside with a certain force. There will be a reaction equal and opposite to this force that will make the milk carton start to spin.

This is a typical example of water turbine that is used to demonstrate the third Newton's law.

The center is basically the heart of it

Wavelength divides in half and speed stays the same.