Thrust and Pressure
Thrust and Pressure
Thrust and Pressure- Thrust and the pressure both of these quantities you will have studied in your earlier classes. Somehow many of the students confuse while defining pressure. Is pressure a force on per unit area or thrust on per unit area? Actually both definitions of pressure is correct. Thrust and force both are the same things but there is a slight difference between thrust and force, actually, thrust is directed to a particular direction and it is a reactive force caused by the surroundings. As an example, if you push and pull a thing then here it is better to use the world force. Actually the term thrust is originated from Newton’s third law,in short thrust is the reaction against a force. A balloon is lifted up to the sky because of a thrust developed due to the pressure difference between the air inside the balloon and the air above it.
is an upward force applied by a surface to a body in contact, which is perpendicular to the surface. At the situation when you stand up, strolling or have various stances what are the forces that keep your balance in these positions while as we probably are aware the gravity acts downwards. When the object is partially or completely submerged into the fluids an upward force is exerted by the fluid on the object which is opposite in direction of the gravitational force, this upward force is known as thrust or buoyant force. This upward thrust generated because of the pressure difference between the upper and lower end of the object as we know the pressure is directly proportional to the depth in a liquid. The case when an object is kept on a surface the gravity acts downwards and as we know that every action has an equal and opposite reaction, this reaction is nothing but an upward force acts on the object by the surface that balances the object in its place.
Thrust or force per unit area is known as pressure
Atmospheric Pressure. Atmospheric pressure is the thrust or weight of the air exerted on per unit surface area of the earth.
1 atmospheric pressure = 101325 Pa which is equivalent to 760 mm Hg
The pressure in a liquid– The pressure in a point within the liquid depends on how much weight of the liquid is above that point, as the depth increases the number of preceding layers of liquid increases and thus weight of the liquid also enhances, it is that’s why with the depth the pressure of the liquid also increases.
Let the depth of a point in a liquid = h, the density of the liquid is =ρ, gravitational acceleration = g, Weight of the liquid above the point = W, Mass of the liquid above the point = m, Area of the cross-section of the container at the point = A
Weight of the liquid above the point = mass of the liquid above the point × gravitational acceleration
W = mg = ρVg
Area of cross-section of the container = A = V/h
S.I Unit of Pressure.
Pressure = Force/Area = Newton/meter²
1 Newton/meter² = 1 Paskal = 1Pa
Numerical questions based on pressure and thrust.
Q1.A cuboidal box of the dimension 20 cm × 15 cm × 10 cm, lying on a table in a position that its largest cross-sectional face is in contact with the table, find the pressure exerted by the box to the table if the mass of the box is 1.2 kg.
Ans. We are given the dimension 20 cm × 15 cm × 10 cm, The face with largest cross-sectional area = 20cm×15cm
Therefore the pressure exerted by the face, 20cm×15cm to the table is = 392 Pa
Q2. A cow of the mass 400 kg is stood on a single leg, if the area of its leg is 20 cm², find the pressure exerted by its leg to the ground.
Ans. Area of the leg, A = 20 cm² = 0.0020 m², mass of the cow, m = 400 kg
Weight = mg = 400 × 9.8 = 3920.0 N
The area exerted by the leg to the ground =1960000 Pa
Q3.A 3 m height container, sealed, is half-filled by fluid. The density of the fluid is ρ = 1.5 Kg/m3. What is the pressure at the bottom of the container?
Ans. Height of the container = h, Depth of the fluid = h/2= 3/2=1.5 m, the density of the fluid is ρ = 1.5 Kg/m3
Pressure = ρhg = 1.5 × 1.5 × 9.8 = 22.05
Therefore Pressure at the bottom =22.05 Pa
Q4.A 20 m height container is filled with fluid. The container is open. The density of the fluid is ρ = 50 Kg/m3. What is the pressure at the bottom of the container?
Ans. Depth of the fluid = 20m, the density of the fluid is ρ = 50 Kg/m3
Gravitational acceleration, g = 9.8 m/s²
Pressure = ρhg = 50 × 20 × 9.8 = 9800
The pressure exerted by the fluid inside the container at the bottom = 9800 Pa
Since the container is open so atmospheric pressure must also be added applied on top of the container
So, net pressure at the bottom of the container = Atm.pressure + 9800Pa = 101325Pa + 9800Pa= 111125Pa
Study the following important topics also
The second law of motion
The universal law of gravitational force
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