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.

**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 ×
10^{5} 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 *a*_{1} *v*_{1} = *a*_{2} *v*_{2}
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 + v^{2}/2 + gh = constant.

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11th Physics : UNIT 7 : Properties of Matter : Summary - Physics: Properties of Matter |

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