Question: how does liquid flow up a straw?

Chloe Huseyin answered on 13 Nov 2015:

Do you mean when you drink though a straw?

When you suck on a straw to take a drink you create low pressure in your mouth (and in the straw because the straw end inside your mouth is open). The molecules of the drink are under pressure by the atmosphere around them (at the surface of the drink) and they get pushed down into the glass and up the straw to remove this low pressure you made in your mouth. So if you keep sucking and creating the low pressure you continue forcing the drink up the straw (and why when you stop the drink goes back down the straw).