I am studying for the MCAT and I got an interesting question from a Kaplan book: 15. A water tower operator is interested in increasing the pressure of a column of water that is applied to a piston. She hopes that increasing the pressure will increase the force being applied to the piston. The only way to increase the pressure is to alter the speed of the water as it flows through the pipe to the piston. How should the speed of the water be changed to increase the pressure and force? A. Increase the speed B. Decrease the speed C. Release water intermittently against the pipe D. The speed of water will not change pressure at the piston. Correct Answer: B Explanation: This is a basic interpretation of Bernoulli's equation that states, at equal heights, speed and pressure of a fluid are inversely related (the Venturi effect). Decreasing the speed of the water will therefore increase its pressure. An increase in pressure over a given area will result in increased force being transmitted to the piston. This one is interesting to me, because I was sure the answer they wanted was B, because MCAT examiners and book writers love the relationship between velocity and pressure. I am very aware of the inverse relationship between speed and pressure in fluids. However, I don't like this question, because of the fact that water operating a piston is going to push directly on the piston, and it is going to dramatically lose velocity as the kinetic energy is converted to work on the piston: So in this case, I feel like the speed of the water would not have a dramatic effect on the pressure at the piston, for the simple reason that the speed at the piston will be determined by how fast the piston is moving, not how fast the water was released. I feel like if the only thing that can be varied is the initial speed of the fluid, and the fluid will almost stop, the only effect on pressure at the piston will be the mass of the fluid itself. Is my intuition on this flawed, is it the case that releasing the water much faster will result in a lower final pressure on the piston? Possibly the issue here is that I am thinking about the final pressure, not the instantaneous pressure the moment the fluid touches the piston. Obviously, at the moment it touches the piston, the fluid would have a lower pressure that the same fluid moving slower, but this is a dumb comparison because if the fluid were moving slower there would be less of it in that instant anyway.