# Straw sucking height calculation

by paulfr
Tags: calculation, height, straw, sucking
 P: 175 How high can one suck water up a straw ? Is this analysis and calculation correct ? ================ Straw sucking height limit calculation Sucking up thru a straw from a height ...limit h = ? m If the pressure P [=F/A] , the work done to lift the water column to h is W = F dot s = PA x h/2 [average height = h/2] The potential energy of the column is PE = ρAhg (h/2) [c of m is in the middle]. When the column rises up to its highest, there is no motion, so all the energy is potential. Equating work done to potential energy due to energy conservation PAh/2 = ρAhg (h/2) P = ρhg h = P / ρ g h = 1.0e5 N/m^2 / (1000 kg/m^3) ( 10 m/s^2) h = 10 meters Does that look correct ? Thanks for your comments
 HW Helper Sci Advisor Thanks P: 9,025 What you have answered is what height column of water would balance a given pressure difference. There are additional constraints if you are thinking of a human sucking on the end ... like the capacity of the lungs. How long would it take for a human to suck up a 10m column of air through a straw? Against the resistance of having to pull up that mass of water? Then I'd want to ask if the human lungs could do that much work - I suspect that will be the limiting factor. You'll find that the area of the straw matters ... compare sucking through a drinking straw and a hose pipe.
 Mentor P: 9,593 Well, you can make the straw thin to lower the volume, or do it in several steps. The limited pressure difference of the lungs is more problematic - lungs are not good vacuum pumps.
HW Helper