Fluids -- evacuated chambers I've worked on this problem in a few different ways. Maybe I'm having trouble with the direction of my forces: We have a an evacuated chamber the pressure inside of the chamber is 23.0 kPa a 5cm diameter hole covered by a 0.225m diameter circular panel (mass is negligable) And the question asks for the force required to pull off the panel. My first thinking was that because the "vacuum" is being caused by the pressure of the atmosphere, I'm calling it Fair, is the force pointing down on the panel The force of the air inside the chamber is pushing up through the 5cm diameter hole on a small section of panel Fc, and the pulling force required to take off the panel is upwards, Fp. So, Fnet = Fp + Fc - Fair = 0 Fp = Fair - Fc Fc = PA = 23000*pi*r^2 = 45.16 N where r is the radius of the hole in the chamber Fair = 101300*pi*R^2 = 4028 N where R is the radius of the panel And then I'd solve for Fp. But my answer -- 3982.61 N -- was incorrect. I'm obviously missing something critical. Would you have any ideas of what I'm doing wrong, and maybe point me in the right direction? Thanks!