Summary - Physics: Properties of Matter

SUMMARY

The force between the atoms of an element is called inter-atomic force whereas the force between the molecules of a compound is called inter-molecular force.

Hooke’s law: within the elastic limit, the stress is directly proportional to strain.

The force per unit area is known as stress. If F is the force applied and A is the area of cross section of the body then the magnitude of stress is equal to F/A. Tensile or compressional stress can be expressed using a single term called longitudinal stress.

The ratio of change in length to the original length of a cylinder is ∆L/L, which is known as longitudinal strain

Within the elastic limit, the ratio of longitudinal stress to the longitudinal strain is called the Young’ s modulus of the material of the wire.

Within the elastic limit, the ratio of volume stress to the volume strain is called the bulk modulus.

Within the elastic limit, the ratio of shear stress to the shear strain is called the rigidity modulus.

Poisson’s ratio = lateral strain/longitudinal strain

The elastic potential energy stored in the wire per unit volume is

U = 1/2 × stress × strain= 1/2 × Y × (strain)2 , where Y denotes Young’s modulus of the material.

If F is the magnitude of the normal force acting on the surface area A, then the pressure is defined as the ‘force acting per unit area’.

The total pressure at a depth h below the liquid surface is P = P_a + ρgh, where P_a is the atmospheric pressure which is equal to 1.013 × 10⁵ Pa.

Pascal’s law states that the pressure in a fluid at rest is the same at all points if they are at the same height.

The law of floatation states that a body will float in a liquid if the weight of the liquid displaced by the immersed part of the body is equal to or greater than the weight of the body.

The coefficient of viscosity of a liquid is the viscous force acting tangentially per unit area of a liquid layer having a unit velocity gradient in a direction perpendicular to the direction of flow of the liquid.

When a liquid flows such that each particle of the liquid passing a point moves along the same path and has the same velocity as its predecessor then the flow of liquid is said to be streamlined flow.

During the flow of fluid, when the critical velocity is exceeded by the moving fluid, the motion becomes turbulent.

Reynold’s number has a significance as it decides which decides whether the flow of fluid through a cylindrical pipe is streamlined or turbulent.

Stokes formula F = 6πηav, where F is the viscous force acting on a sphere of radius a and v is the terminal velocity of the sphere.

The surface tension of a liquid is defined as the force of tension acting on a unit length of an imaginary line drawn on the free surface of the liquid, the direction of the force being perpendicular to the line so drawn and acting parallel to the surface.

The angle between tangents drawn at the point of contact to the liquid surface and solid surface inside the liquid is called the angle of contact for a pair of solid and liquid.

The flow of a fluid is said to be steady if, at any given point, the velocity of each passing fluid particle remains constant with respect to time.

The equation a₁ v₁ = a₂ v₂ is called the equation of continuity for a flow of fluid through a tube and it is due to the conservation of mass in the flow of fluids. It states that the sum of pressure energy, kinetic energy, and potential energy per unit mass of an incompressible, non-viscous fluid in a streamlined flow remains constant. i.e., P/ρ + v²/2 + gh = constant.