But when we turn the nail over, and hit it on the point, the force is distributed over a much larger area. The force is now distributed over the surface of the wood that touches any part of the nail head. As a result, the pressure applied to the wood is much smaller and the nail just bounces off the wood. Click here to check your answer to Practice Problem 1. Click here to see a solution to Practice Problem 1.
Most people expect the height of the columns of liquid in the two arms of the tube to be the same.
Experimentally, we find the results shown in the figure below. A column of water 100 cm tall exerts a pressure of 100 grams per square centimeter. A column of ethyl alcohol 127 cm tall exerts the same pressure. Because the pressure of the water pushing down on one arm of the U-tube is equal to the pressure of the alcohol pushing down on the other arm of the tube, the system is in balance. This demonstration provides the basis for understanding how a mercury barometer can be used to measure the pressure of the atmosphere.