Question

It is well known that you can trap water in a drinking straw by placing the tip of your finger over the top
while the straw is in the water, and then lifting it out. The inner diameter of the straw is 0.5 cm; the
height of the trapped water column inside the straw is 5.0 cm. Find the pressure in the air pocket
between your finger and the water

Answer 1

$\fn_jvn \rho_{water} = 1000\;kg/m^3\\ volume\;of\;the\;trapped\;water = \pi*r^2*h\\ r = 0.0025\;m\\ h = 0.025\;m\\ Pressure = \rho*g*h = 1000*9.8*0.025 = 245\;Pa$