Setup: A long tube is filled with red-colored water. One end of the tube is held out side the tank, level with the water in the tank. While the other end remains under water, the middle of the tube is lifted to the ceiling. Then the end of the tube is lowered to create a siphon.

Observations:  

• The first part of the demo is another example of Pascals's Principle. The pressure of the atmosphere is transmitted undiminished throughout the water even if some of the water is in a tube that is above the level of the water in the tank. The atmospheric pressure is the same on both the water in the end of the tube outside the tank and on the water at the top of the tank.
• The maximum height that the tube could be raised is 10.3 m, the height of a collom of water that has the same pressure as standard atmospheric pressure.
• When the tube out side the tank is lowered below the level of the water in the tank, the hydrostatic pressure of the water in the tube become greater than that at surface of the tank (which is atmospheric pressure) because it is a lower level, P = r gh +P_a
• The lower the level of the outside tube, the faster the water will flow out the tube because of the greater pressure. In this demo the flow is fairly slow because of the friction of the water in the long tube with the walls of the tube. Bernoulli's equation shows that the maximum flow rate would equal to that of an object falling freely from the level of the water in the tank to end of the tube.