Due to the 17th century does not exist when the toothpaste tube. Therefore, it is suspected bleise Pascal (Blaise Pascal, 1623 - 1662, the French famous scientists and philosophers) is put forward the principle of Pascal, whether every morning in wrestling with the function of it.
However, it is certain that many of the other effects related to the liquid static pressure can not escape his attention, the first is the principle of hydraulic crane.
A long time ago, engineers will use this type of machine. Today, as long as in the parking lot or the gas station, you can see the hydraulic crane, use it resorted to a child's strength will be able to lift a car up. Let's see how the device works, and try to make an instrument for the experiment.
Please see figure 2. Use a tube to connect the two containers filled with liquid (water or oil). One of the containers is very large, and the section of the other vessel is small, assuming that it is 1000 times smaller than the previous one. If you use a piston (a) pressing down on the small section of the liquid level in the tank, liquid is a pressure, stress and the intensity will according to the size of the original transfer to any other part of the liquid surface, including, of course, in the liquid container of large cross section and piston (b) contact surface. Pressure is equal to the force divided by the area of action.
According to the Pascal principle, the pressure of piston B and the pressure of the piston under A are equal, and the area under the piston B is 1000 times larger than that of the piston under A, the acting force on it should be 1000 times larger than that on the A. Therefore, in order to lift a 1 ton car, as long as 1 kg of force is enough. Hydraulic brake, compressor, car jack, pump and many other instruments have benefited from this principle.
A small experiment to verify the theory of Pascal
We can make a small hydraulic device at home by using two syringes with a needle out of the needle.
For example, with a cross section of 5 square centimeters of blood transfusion with a thick syringe and a section of 0.5 square centimeters of a very small syringe, the opening of them with a thick and short pipe to connect. According to Pascal principle, the transformation coefficient of force is about 10. Fill the syringe with water, oil or other liquids, all of the space between the two pistons. Then ask your friend with the thumb squeeze a two piston, and you squeeze another piston with the thumb. We can call this little game "the iron thumb contest", or "Pascal thumb contest". Of course, who squeeze a small syringe, who will not take the effort to win. If you have certain creativity and do the experiment, you can use a spring ergometer or say things the scales (as shown in Figure 3), trying to measure in extrusion of two pistons (or with a weight ratio of piston and injector tube wall between the friction force of weight) the applied pressure, check Pascal's principle, take a look at the pressure on both sides are equal. Don't forget to subtract the value from the value that has been measured from the test to the active part of the system, which is the weight of the piston.
Finally, if you want to verify efficiency of as a pressure device, the device can be placed between the scale plate and the big piston on a walnut: you will see squeeze a small syringe piston can easily be crushed walnut.
With this small machine will be able to complete the "Haig Lis" (Jose's son, the power of infinity, had completed 12 heroic achievements) so great. Prepare a full liquid filled barrel (do not have air, because the air will be compressed under pressure), you can begin to show your friends. Will be filled with a liquid filled with a liquid filled with a small syringe and a small tube connected, you will see the latter two can be shattered in the barrel. We try to calculate brushstroke Zhang: a section for 0.5 cm2 ordinary syringe, with the thumb applied pressure on the piston is 20 kilograms (with scale validation, achieves this weight is not difficult), the pressure was actually 40 ATM. Few barrels can withstand such pressure. A farmer was sorry to find this phenomenon. He wanted to pass a long thin tube of precious wine from his country cottage to a friend at the foot of the mountain at the foot of 30 meters. Everything was going well: Friends of the casks filled with wine, but then the pressure in the liquid pipe soon the bucket crusher, wine soaked up the house.