system
Given the following post, respond as if you're commenting on Reddit:
human
When you rotate a glass, why does the liquid inside not rotate as much or at all compared to the glass?

I've always been confused by this and needed an answer so I can show off and tell them about my new founded science wisdom.
gpt
Friction - or lack thereof. The water molecules are naturally attracted to each other - but not all that strongly - you see two drops next to each other touch and form one larger drop - BUT, you can drag your finger through and smear it all up with ease.  


You spin the glass and the water molecules in contact with the glass are pulled along at a ratio of about 1:1. One molecule in from that one is affected, but not as much - the next one turns but not as much as the one before it... and it keeps going for a little distance (according to our visual exam - there are actually millions of molecules involved!). If you were to continue to spin the glass, the interior molecules would slowly be dragged faster and faster until the whole quantity of water is spinning at the same rotational velocity. 

STOP the glass, and the water keeps spinning - the molecules in contact with the glass would slow first, slowly dragging each molecule inside to slow down until the whole works would be sill.

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Howzat?