Liquids and gases can flow and are therefore, called fluids. The volume of solid, liquid or gas depends on the stress or pressure acting on it. The difference between gases and solids or liquids is that for solids or liquids the change in volume due to change of external pressure is rather small.
Solids and liquids have much lower compressibility as compared to gases. Shear stress can change the shape of a solid keeping its volume fixed. The key property of fluids is that they offer very little resistance to shear stress; their shape changes by application of very small shear stress. The shearing stress of fluids is about million times smaller than that of solids.
Pressure: Smaller the area on which the force acts, greater is the impact. This concept is known as pressure.
When an object is submerged in a fluid at rest, the fluid exerts a force on its surface. This force is always normal to the object’s surface. If there were a component of force parallel to the surface, the object will also exert a force on the fluid parallel to it; as a consequence of Newton’s third law. This force will cause the fluid to flow parallel to the surface.
Since the fluid is at rest, this cannot happen. Hence, the force exerted by the fluid at rest has to be perpendicular to the surface in contact with it. This is shown in Figure.a.
The normal force exerted by the fluid at a point may be measured. An idealised form of one such
pressure-measuring device is shown in Fig.b. It consists of an evacuated chamber with a spring that is calibrated to measure the force acting on the piston. This device is placed at a point inside the fluid. The inward force exerted by the fluid on the piston is balanced by the outward spring force and is thereby measured.
If F is the magnitude of this normal force on the piston of area A then the average pressure Pav
is defined as the normal force acting per unit area.
Pressure is a scalar quantity.
Related posts :
Bulk Modulus
Shear modulus
Elastic behavior of Solids
Stress and strain
Stress and Strain Curve
Determination of Young's modules
Solids and liquids have much lower compressibility as compared to gases. Shear stress can change the shape of a solid keeping its volume fixed. The key property of fluids is that they offer very little resistance to shear stress; their shape changes by application of very small shear stress. The shearing stress of fluids is about million times smaller than that of solids.
Pressure: Smaller the area on which the force acts, greater is the impact. This concept is known as pressure.
When an object is submerged in a fluid at rest, the fluid exerts a force on its surface. This force is always normal to the object’s surface. If there were a component of force parallel to the surface, the object will also exert a force on the fluid parallel to it; as a consequence of Newton’s third law. This force will cause the fluid to flow parallel to the surface.
Since the fluid is at rest, this cannot happen. Hence, the force exerted by the fluid at rest has to be perpendicular to the surface in contact with it. This is shown in Figure.a.
The normal force exerted by the fluid at a point may be measured. An idealised form of one such
pressure-measuring device is shown in Fig.b. It consists of an evacuated chamber with a spring that is calibrated to measure the force acting on the piston. This device is placed at a point inside the fluid. The inward force exerted by the fluid on the piston is balanced by the outward spring force and is thereby measured.
If F is the magnitude of this normal force on the piston of area A then the average pressure Pavis defined as the normal force acting per unit area.
Pressure is a scalar quantity.
Related posts :
Problems on Bernoulli's theorem and Its Applications
Shear modulus
Elastic behavior of Solids
Stress and strain
Stress and Strain Curve
Determination of Young's modules
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