Name some of the devices which use liquid pressure and the principle behind them.Also why liquid pressure is preferred over other ways of exerting force.
Devices that use liquid pressure are :-
Manometer
- A device that measures fluid pressure.
A manometer works on the principle of hydrostatic equilibrium and is used for measuring the pressure (static pressure) exerted by a still liquid or gas. Hydrostatic equilibrium states that the pressure at any point in a fluid at rest is equal, and its value is just the weight of the overlying fluid. In its simplest form, a manometer is a U-shaped tube consisting of an incompressible fluid like water or mercury.
SPHYGMOMANOMETER
- Used to measure human blood pressure.
A sphygmomanometer, blood pressure meter, blood pressure monitor or blood pressure gauge (also referred to as a sphygmometer) is a device used to measure blood pressure, composed of an inflatable cuff to collapse and then release the artery under the cuff in a controlled manner, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. Manual sphygmomanometers are used in conjunction with a stethoscope.
A sphygmomanometer consists of an inflatable cuff, a measuring unit (the mercury manometer, or aneroid gauge), and a mechanism for inflation which may be a manually operated bulb and valve or a pump operated electrically.
MERCURY BAROMETER:
- Used to measure atmospheric pressure.
A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short term changes in the weather. Numerous measurements of air pressure are used within surface weather analysis to help find surface troughs, high pressure systems and frontal boundaries.
The principle on which the barometer is based may be explained in the following manner. If you put one end of a tube into a bowl of water and the other end into your mouth, you can draw the water up through the tube into your mouth by sucking. You may think that you suck the water up, but you do not; you merely suck the air out of the tube by means of the muscles of your mouth. The weight of the outer air then presses down on the water in the bowl and forces it up into the tube. As soon as you let the air into the tube again the water runs back into the bowl. If you had a tube 40 ft. in length and could suck all the air out of it, the water would rise up in the tube nearly 34 ft. It would stop at that height, because the weight of the column would just balance the weight of the air which presses down on the surface of the bowl. As the tube is more than 34 ft. long, in the space above the water, there would be nothing, not even air. Such a space is called a vacuum, from the Latin word meaning space without air. If you put the tube into a fluid lighter than water, such as alcohol, the alcohol will rise higher in the tube than 34 ft., because it will take more fluid to balance the weight of the air. If the fluid were heavier than water, as is quicksilver or mercury, it would not rise so high, because it would require less of it to equal and balance the weight of air.
And liquid pressure is preferred over force because in case of liquid or fluid contact is very smooth, hence force per unit area, i.e. pressure is preferred over force.
Manometer
- A device that measures fluid pressure.
A manometer works on the principle of hydrostatic equilibrium and is used for measuring the pressure (static pressure) exerted by a still liquid or gas. Hydrostatic equilibrium states that the pressure at any point in a fluid at rest is equal, and its value is just the weight of the overlying fluid. In its simplest form, a manometer is a U-shaped tube consisting of an incompressible fluid like water or mercury.
SPHYGMOMANOMETER
- Used to measure human blood pressure.
A sphygmomanometer, blood pressure meter, blood pressure monitor or blood pressure gauge (also referred to as a sphygmometer) is a device used to measure blood pressure, composed of an inflatable cuff to collapse and then release the artery under the cuff in a controlled manner, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. Manual sphygmomanometers are used in conjunction with a stethoscope.
A sphygmomanometer consists of an inflatable cuff, a measuring unit (the mercury manometer, or aneroid gauge), and a mechanism for inflation which may be a manually operated bulb and valve or a pump operated electrically.
MERCURY BAROMETER:
- Used to measure atmospheric pressure.
A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short term changes in the weather. Numerous measurements of air pressure are used within surface weather analysis to help find surface troughs, high pressure systems and frontal boundaries.
The principle on which the barometer is based may be explained in the following manner. If you put one end of a tube into a bowl of water and the other end into your mouth, you can draw the water up through the tube into your mouth by sucking. You may think that you suck the water up, but you do not; you merely suck the air out of the tube by means of the muscles of your mouth. The weight of the outer air then presses down on the water in the bowl and forces it up into the tube. As soon as you let the air into the tube again the water runs back into the bowl. If you had a tube 40 ft. in length and could suck all the air out of it, the water would rise up in the tube nearly 34 ft. It would stop at that height, because the weight of the column would just balance the weight of the air which presses down on the surface of the bowl. As the tube is more than 34 ft. long, in the space above the water, there would be nothing, not even air. Such a space is called a vacuum, from the Latin word meaning space without air. If you put the tube into a fluid lighter than water, such as alcohol, the alcohol will rise higher in the tube than 34 ft., because it will take more fluid to balance the weight of the air. If the fluid were heavier than water, as is quicksilver or mercury, it would not rise so high, because it would require less of it to equal and balance the weight of air.
And liquid pressure is preferred over force because in case of liquid or fluid contact is very smooth, hence force per unit area, i.e. pressure is preferred over force.
