# Hydrodynamics lab question

im supposed to predict height as a function of time for water leaving an orifice. determine heaigh as a function of drain time experimentally and compare the two on the same graph.

i dont even understand what it wants. im pretty sure ive got all the necessary data, but i dont know how to do what he wants.

okay, i think i have some of it figured out. but i dont know what formula to use to predict predict height as a function of time for water leaving the orifice.

heres what im doing. please correct it because this is driving me insane.

im using V/t= AV. this is just different forms of the flow rate. i know the amount of (volume) of water i am gathering. it is 100 ml. i wanna know how long it takes to get this amount. my lab partner found the area of the orifice to be about .15 cm^3. and im using (2*g*h)^1/2 as the velocity. using this i end up with a time of about 357 seconds for 18 cm of height. so i checked the area of orifice using my collected data. for 100 ml of water to be collected, it too approx 4.06 sec. this is at 18 cm of height. using this, the area was around 46.
what am i doing wrong?

turin
Homework Helper
formulajoe,
what level of physics is this?

There could be a (simple) differential equation involved here. The flow rate at the oriface will be determined by the pressure at the level of the oriface below the water's surface. This will of course change with time. if the amount of water that you are extracting doesn't change the water level significantly (i.e. if the reservior is very wide), then this is probably not the case.