Fluid is typically defined as any substance that cannot maintain a shearing or tangential force when it is at rest. It goes through continuous variation in shape when exposed to such stress. The major characteristic of fluids is the constant position change of one section of the material relative to different parts under shear stress. On the other hand, consider shearing forces in elastic solids that are held in a flexed or twisted orientation; such solids do not undergo flow and can easily revert back to their original shape. Compressed fluids can come to their stable shape, but the forces between the container and fluid or forces within the fluid should not be shear forces. The fluids apply an outward pressure known as hydrostatic pressure that is predominantly perpendicular to the container’s surface.
Fluid Pressure
Fluid pressure is the measure of the force exerted by the fluid per unit area on a body in the fluid or on the closed container’s surface. This pressure can be generated by any acceleration or by outside forces on the closed container. Such fluids have no distinct shape, and their pressure is exerted in every direction. This pressure can be enhanced through variations in the fluid’s velocity and hydraulic processes. In the case of water in a lake, pressure at the lake’s bottom is approximately equivalent to the weight of the water column divided by the column’s area. When a person stands on a pool’s bottom (without floating), there will be a water column of about the diameter of the person’s head all the way up to the bottom, pushing the whole body down. The value of fluid pressure on the head can be calculated by dividing the weight of the water column by the weight of the area of the head. Normally, to counter the external pressure, the human body raises the internal body pressure according to the external forces engulfing the body. As the depth increases, the water pressure can be very high, and after some point, the human body will not be able to withstand the pressure.
In the case of atmospheric pressure, dividing the weight of the air column by the area of the top of the person’s head gives the air pressure on the top of the head. When a weather report shows high pressure, this implies that the air column reaches up higher than it reaches for lower air pressure readers. A barometer calculates the weight of the air column or the air pressure. This type of pressure is created by the weight of all the air many miles above the affected body. Even though this pressure is very high, human bodies generate enough internal pressure that balances out the air pressure. The average air pressure in Delhi is less than in Leh. This is due to the higher altitude of Leh, which implies that its air column is not as tall as in Delhi. This also implies that a pressurised snack pack (made in Delhi) will expand when it is brought to Leh. As it is brought to a lower pressure area, it may even explode as per the extent of the condition.
Fluid Pressure Effects
The main quantities that impact fluid pressure are heating, motion, and chemical changes. The motion of fluids such as rivers, wind and sea waves can exert pressure on objects proportional to the surface area perpendicular to the motion’s direction. A streamlined shape decreases the effective pressure on the submerged objects. When fluids are heated, it generally expands. If fluids are heated inside an enclosed vessel, the expansion will attract more internal pressure. Heating balloons will cause them to expand. Chemical reactions that release gases will raise the pressure inside a vessel. In many cases, chemical reactions will speed up if there is a variation in fluid pressure. Shaking a carbonated beverage will increase the production of gases and the fluid pressure inside the bottle.
Daniel Bernoulli found out that the air pressure in a pipe decreases when the air velocity in the pipe increases. This is called Bernoulli’s Principle. One of the best applications of this concept is employed in aeroplanes and other flying crafts. The wings of aeroplanes are typically flat on the bottom and curved on the top. When air travels over the curved top section of the wing, the speed increases due to the speciality of the shape. This directly reduces the pressure relative to the bottom section of the wing. The less pressure on the top part produces the lift needed to maintain the aeroplane in ideal motion.
This video explains the application of Bernoulli’s principle
Important Fluid Pressure Questions with Answers
1) What is meant by pressure?
Pressure is the force exerted perpendicular to the surface of a body per unit area along which that force is applied.
2) What are the main types of pressures?
Absolute pressure, gauge pressure, differential pressure and sealed pressure are the main types of pressure.
3) What is meant by gauge pressure?
Gauge pressure is defined as the pressure relative to the ambient pressure.
4) What is fluid?
A fluid is a gas, liquid or other substance that constantly deforms under an applied external force. An ideal fluid has practically zero shear modulus. In simpler terms, they are materials which cannot withstand any type of shear force exerted on them.
5) What are the main types of fluids?
The main types of fluids are steady or unsteady, compressible or incompressible and viscous or non-viscous.
6) What is meant by fluid pressure?
Fluid pressure is the measure of the force exerted by the fluid per unit area on a body in the fluid or on the closed container’s surface. This pressure can be generated by any acceleration or by outside forces from the closed container. Such fluids have no distinct shape; their pressure is exerted in every direction. This pressure can be enhanced through variations in the fluid’s velocity and hydraulic processes.
7) What are the impacts of fluid pressure?
The impacts of fluid pressure are heating, motion, and chemical changes. The motion of fluids such as rivers, wind and sea waves can exert pressure on objects proportional to the surface area perpendicular to the motion’s direction. A streamlined shape decreases the effective pressure on the submerged objects. When fluids are heated, it generally expands. If fluids are heated inside an enclosed vessel, the expansion will attract more internal pressure. Heating balloons will cause them to expand.
8) Give an example of variation of fluid pressure between two places with different altitudes.
The average air pressure in Delhi is less than in Leh. This is due to the higher altitude of Leh, which implies that its air column is not as tall as in Delhi. This also implies that a pressurised snack pack (made in Delhi) will expand when it is brought to Leh. As it is brought to a lower pressure area, it may even explode as per the extent of the condition.
9) The fluids apply an outward pressure known as _____ pressure that is predominantly perpendicular to the container’s surface.
Answer: hydrostatic
Explanation: The fluids apply an outward pressure known as hydrostatic pressure that is predominantly perpendicular to the container’s surface.
10) Explain the direction of fluid pressure.
The pressure generated by fluids not only pushes down at a particular point, but also pushes up and to the sides. On every side, pressure is the same. This is due to the nature of gases and liquids to adapt to the container’s shape. This also implies that any hollow vessel immersed in a liquid has pressure on the entire surface, bottom and top. When a person swims underwater, the water pressure increases as the depth increases. The fundamental reason that we do not feel the pressure is the counterpressure produced by our bodies to nullify this crushing force. The body acts like a fully blown balloon under such pressure. As the body goes deeper, the water pressure will increase and will overcome the body’s internal pressure. This will result in fatal health and physical issues.
11) What are the main quantities that impact fluid pressure?
The main quantities that impact fluid pressure are heating, motion, and chemical changes. The motion of fluids such as rivers, wind and sea waves can exert pressure on objects proportional to the surface area perpendicular to the motion’s direction. If fluids are heated inside an enclosed vessel, the expansion will attract more internal pressure. Chemical reactions that release gases will raise the pressure inside the vessel. In many cases, chemical reactions will speed up if there is a variation in fluid pressure.
12) _____ found out that the air pressure in a pipe decreases when the air velocity in the pipe increases.
Answer: Daniel Bernoulli
Explanation: Daniel Bernoulli found out that the air pressure in a pipe decreases when the air velocity in the pipe increases.
13) What is the most familiar application of Bernoulli’s principle?
One of the best applications of Bernoulli’s principle is employed in aeroplanes and other flying crafts. The wings of aeroplanes are typically flat on the bottom and curved on the top. When air travels over the curved top section of the wing, the speed increases due to the speciality of the shape. This directly reduces the pressure relative to the bottom section of the wing. The less pressure on the top part produces the lift needed to maintain the aeroplane in ideal motion.
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Practice Questions
1) What is Bernoulli’s principle?
2) What is meant by hydrostatic pressure?
3) What is hydraulics?
4) What is the average atmospheric pressure?
5) What is viscosity?
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