Page 301 - General Knowledge

GENERAL KNOWLEDGE 2019

the lamina about two mutually perpendicular axes lying in the plane of lamina and
intersecting each other at the point where the perpendicular axis passes through the body.

 Parallel axes theorem: It states that moment of inertia of a body, about an axis, is equal to
the sum of the moment of inertia of the body about a parallel axis through its center of
gravity and the product of the mass of body and the square of the distance between the two
axes.

 Here, is the moment of inertia of the body about an axis through its center of gravity G.

Newton‘s law in rotational motion
 First Law: It states that everybody continues in its state of rest or of uniform rotational
motion about a given axis unless it is completed by some external unbalanced torque to
change that state.
 Second Law: It states that the rate of change of angular momentum of a body is directly
proportional to the impressed torque and takes place in the direction of torque.
 Third Law: It states that to every torque there is an equal and opposite torque.

Gravitation
 Every object in the universe attracts every object with a force which is called the force of
gravitation.
 Gravitation is one of the four classes of interactions found in nature. These are
 The gravitational force
 The electromagnetic force
 The strong nuclear force
 The weak nuclear forces
Universal Law of Gravitation
 It states that any two bodies having mass attract each other with a force directly proportional
to the product of their mass and inversely proportional to the square of distance between
them.
 The force acts along the line joining the centres of the objects.
Importance of Gravitational Force

 It binds us to Earth.
 Moon revolves around Earth due to gravitational force. Planets revolve around Sun due to
gravitational force.
 Tides in seas are caused due to gravitational force of moon on earth.

5. PROPERTIES OF MATTER
 Matter may exist in the solid, liquid or gaseous states.
 Although on the microscopic level all matter is made up of atoms or molecules, everyday
experience tells us that the three states have very different properties.
 This set of lectures is aimed at examining these properties and the underlying physics
behind them.
 Solids are composed of atoms held together by attractive or cohesive forces.
 If the cohesive forces are strong, the atoms are tightly bound to one another and the matter
is in the solid state.

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