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Pressure in Liquid is the pressure that develops at a particular point within a liquid due to its weight.
- Fluid Pressure is the measurement of the force per unit area acting on an object in the fluid.
- It is caused due to various factors such as Gravity, Acceleration, or Forces outside the closed container.
- Changes in the fluid's velocity and hydraulic systems lead to an increase in the pressure in liquid.
- Pressure in liquid rises together with the depth.
- The pressure is applied in all directions as fluids have no definite shape.
Read More: NCERT Solutions For Class 11 Physics Mechanical Properties of Fluids
Key Terms: Pressure in Liquid, Fluid Pressure, Fluid Density, Fluids, Force, Pressure, Motion, Molecules
What is Pressure in Liquid?
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Pressure in Liquid is the pressure at a point within a fluid arising due to the weight of the fluid.
- It is affected by the changes in the velocity of the fluid and hydraulic mechanisms.
- The particles of fluids are constantly moving in all directions.
- They bump into each other due to their constant motion.
- Pressure is exerted by these collisions equally in all directions.
- In the case of liquids, the pressure increases as the depth increase.
- It happens because as one goes deeper, fluid at a lower depth will support fluid that is above it.
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How to Measure Fluid Pressure?
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Fluid pressure is a force that results from the random and constant motion of molecules. When a fluid is at rest, a force perpendicular to every surface it comes into touch with is exerted.
- The unit of measurement for pressure in liquid is Pascal (Pa).
- One Pascal is equivalent to one Newton per square meter (N/m2).
- Pressure in Liquid is a function of gravity, depth, and the density of the liquid.
- Since the density of the liquid and gravity are constant, the largest factor is the depth of the liquid.
Fluid Pressure Formula
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Pressure in Liquid or Fluid Pressure Formula is given as
Pfluid = ρgh
Where
- g: Acceleration due to Gravity,
- h: Height (Depth) of Liquid
- ρ: Density of Liquid
| Solved Example Example: A fluid is 5.00 m high and has a density of 1.08 x 103 kg/m3. The acceleration due to gravity on earth is given as 9.81 m/s2. What will be the Fluid Pressure? Solution: Given that,
Using the Fluid Pressure Formula, Pfluid = ρgh Pfluid = 1.08 x 103 x 9.81 x 5 Pfluid = 5.30 x 104 Thus, the fluid pressure is 5.30 x 104 Pa. |
Read More: Mechanical Properties of Fluids Important Questions
Calculation of Fluid Pressure
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Fluid Pressure is calculated using the formula:
Pfluid = P + ρgh
Where
- Pfluid: Pressure at a point in a fluid
- P: Pressure at the reference point
- ρ: Density of the fluid
- g: Acceleration due to gravity (g = 9.8 m/s2)
- h: Height from the reference point
The density of a fluid may be estimated by dividing its mass by the volume of fluid taken into account.
ρ = m/V
Where
- m: Mass of the fluid
- V: Volume of fluid considered
If the fluid is subject to atmospheric pressure, then the total pressure on the system is given by
Pfluid = Po + ρgh
Where Po denotes the Atmospheric Pressure.
Read More: Mechanical Properties of Fluids MCQs
Conditions for Calculation of Fluid Pressure
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Fluid Pressure is calculated under the following two conditions:
- Open condition or open channel flow
- Closed conduit or in a closed condition
Hydrostatic Pressure, also referred to as static fluid pressure, is the fluid pressure that is stated above. Because the pressure produced by fluid movement may be considered to be minimal, it is only taken into account here about the fluid's depth.
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Factors Affecting Fluid Pressure
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Fluid Pressure is affected by two factors namely Depth of Fluid, and Density of Fluid.
- Depth of Fluid: Fluid pressure increases as the depth increases.
- Density of Fluid: Denser fluids like water impose higher pressure than lighter fluids.
Things to Remember
- Pressure in Liquid is the force acting per unit area of an object in a fluid.
- Pascal (Pa) is the unit of measurement for Pressure in Liquid.
- Fluid Pressure Formula is given as Pfluid = ρgh.
- Fluid pressure is calculated in Open Channel Flow or Closed Conduit.
- Density and Depth of the fluid are the two factors affecting Fluid Pressure.
- Pressure in Liquids increases with depth and heavier fluids exert more pressure.
Previous Years’ Questions
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Sample Questions
Ques. Find the pressure exerted on a scuba diver at a depth of 12 meters under the ocean's surface if the density of seawater is 1.03 × 103 kg/m3 and the atmospheric pressure is 1.01 × 105 N/m2. (3 Marks)
Ans. Given that
- Density of Seawater = 1.03 × 103 kg/m3
- Atmospheric Pressure = 1.01 × 105 N/m2
Substituting the values in the Fluid Pressure Formula, we get
Pfluid = ρgh = (1.03 × 103 kg/m3) (9.8 m/s2) (12 m) = 1.21 × 105 N/m2
PTotal = Patmosphere + PFluid = (1.01 × 105) + (1.21 × 105) Pa = 2.22 × 102 kPa (kilo Pascals)
Ques. What causes a rise in gas pressure? (3 Marks)
Ans. Gas pressure is influenced by temperature, pressure, volume, and the number of molecules.
- The pressure of the gas rises as the number of molecules in the gas rises.
- The pressure of the gas rises as the volume falls.
- As the temperature rises, the pressure of the gas also rises.
Ques. What are the types of fluid pressure? (3 Marks)
Ans. Dynamic pressure and static pressure are the two kinds of fluid pressure.
- Static pressure is a fluid's pressure that behaves like a potential and is measured as being constant in all directions.
- Dynamic pressure is the force exerted by a flowing liquid. The direction of motion affects dynamic pressure.
Ques. What factors affect Fluid Pressure? (2 Marks)
Ans. The two factors that determine fluid pressure are Fluid Depth and Fluid Density.
- Fluid's Depth: As the depth of the fluid grows, so does the pressure the fluid exerts.
- Fluid's Density: Denser fluids like water exert more pressure than lighter fluids like air.
Ques. What is the unit of measurement for Pressure in Liquid? (3 Marks)
Ans. Pascal (Pa) is the SI unit of measurement for fluid pressure.
1Pa = 1N/m2
Fluid Pressure is calculated using the formula,
Pfluid = ρgh
Where
- h is the depth of the liquid
- ρ is the liquid's density
- g is the acceleration due to gravity
Ques. List the rules governing Pressure in Liquid. (3 Marks)
Ans. The rules governing the Pressure in Liquid are as follows:
- Pressure in Liquid is constant in all directions.
- Pressure in a stationary liquid is constant over the entire horizontal plane.
- As the distance from the free surface increases, pressure at a location inside the liquid rises.
- Different liquids have different pressures at the same depth. It rises in proportion to the liquid's increasing density.
Ques. Explain the Laws of Pressure in Liquid. (3 Marks)
Ans. The laws of Pressure in Liquid are as follows:
- Liquids exert pressure on the walls of the container.
- Pressure force increases with the depth of the liquid.
- Pressure will be the same at all depths and places within the liquid.
Ques. What is the effect of temperature on Gas Pressure? (2 Marks)
Ans. The average kinetic energy and temperature of the molecules of a gas are inversely related. When the temperature increases, the kinetic energy of the gas molecules becomes high, and the collision rate of the particles increases. Thus, the pressure increases across the wall of the container.
Ques. What are the conditions required for the Consideration of Fluid Pressure? (2 Marks)
Ans. The conditions required for the consideration of Fluid Pressure are:
- Open circumstances or open channel flow
- A closed conduit or in a closed state
Ques. What factors affect Fluid Flow? (2 Marks)
Ans. Three factors that affect the fluid flow rate are as follows:
- Viscosity, Density, and Compressibility
- Speed of Flow
- Shape of Surface
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