basic physics concepts important Gk topic for competitive exam Part 1

Basic physics concepts

Basic physics concepts part 1 ---

Physics is the branch of science which deals with the study of matter, energy, and the interaction between them.

  • A scalar is a physical quantity that has only a magnitude (size) E.g. : Distance, speed, time, power, energy, etc.
  • A Vector is a physical quantity that has both a magnitude and a direction. E.g. Velocity displacement, acceleration, force etc.
    Some physical quantities like moment of inertia, stress, etc. are neither scalar nor vector. They are tensor.

Seven fundamental Physical Quantities and their Units

(Physical Quantity --- SI Unit --- Symbol)`

  • Length --- Meter --- M
  • Mass --- Kilogram --- Kg
  • Time --- Second --- S
  • Electric --- Current Ampere --- A
  • Temperature --- Kelvin --- K
  • Luminous ---- intensity candela ---- Cd
  • Amount of substance Mole --- mol

Some derived Physical Quantities and their Units

(S. No -- Physical -- Quantity -- Cgs Unit -- SI Unit -- Relation)
1. Force -- Dyne -- Newton -- 1 newton = 105 dyne
2. Work -- Erg -- Joule -- 1 joule = 107 erg


  • First law of Motion – An abject at rest will remain at rest or in uniform motion remains in uniform motion unless acted on by an external unbalanced force. This law is often called the law of inertia. i.e., resistance to change.
  • Second law of Motion – The rate of change of momentum of a body is directly proportional to the unbalanced external force applied on it.
  • Third law of Motion – For every action there is an equal and apposite reaction.
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Motion of a body along a circular path is called circular motion.
Centripetal force – while a body is moving along a circular path and external force required to act radially inward.
A pseudo force that is equal and opposite to the centripetal force is called centrifugal force.
Cream separator, centrifugal dryer, etc, work on the principal of centrifugal force.


Force that is created whenever two surfaces move or try move across each other,called Friction.
Friction always opposes the motion or attempted motion of one surface across another surface.
Instances where friction is important Walking, Driving, Picking, Something up, Car brakes.



  • Refers work to an activity involving a force and movement in the direction of the force.
  • The SI unit of work is the joule (J).


Capacity of doing work is called energy.

  • It may exist in potential, kinetic, thermal, electrical, chemical, nuclear, or other various forms.
  • Energy cannot be created or destroyed. It can only be transferred to other objects or converted into different forms. This is Law of conservation of energy.
  • The SI unit of energy is joule.
  • The energy associated with motion is called kinetic energy (K).
  • The energy associated with position is called potential energy (U).
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Conversion of Energy

Dynamo- Mechanical Energy into Electrical Energy.
Electrical Motor- Electrical Energy into Mechanical Energy.
Microphone- Sound Energy into Electrical Energy.
Loud Speaker- Electrical Energy into Sound Energy.
Electrical Bulb- Electrical Energy into Light and Heat Energy.

Solar Cell- Solar Energy into Electrical Energy.


  • Power is the rate of doing work.
  • Work / Time=Power
  • The SI unit of power is joule/second.
  • One horse power = 746 watt.


  • Gravitation is a natural phenomenon by which all physical bodies attract each other.
  • On Earth, gravity gives weight to physical objects employing a downward force to keep them grounded.
  • According to Newton’s theory, the gravitational attraction between the planets and the sun holds the planets in elliptical orbits around the sun.
  • The force of gravity depends upon the object’s mass or the amount of matter in the object.
  • The weight (W) of an object is equal to the mass of the object multiplied by the acceleration due to gravity (g).
    W = mg
  • gtmaximum at poles and gminimum at equator.
  • gmoon = 1/6 gearth
  • The value of ‘g’ decreases with altitude depth from the earth’s surface.
  • g decreases due to rotation of earth.
  • Escape speed (ve) is the minimum speed with which an object just crosses the earth’s gravitation field and never comes back.
  • The escape velocity of Earth is about 11.2 kilometers per second and on moon it is 1.4 km/sec.
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  • A satellite is a smaller object in space which orbits around a larger object Planet in space.
  • It can be either artificial, like the communication or weather satellites that orbit the Earth, or they can be natural, like our moon.
  • A geostationary satellite is an earth orbiting satellite, placed at an altitude of approximately 35,800 kilometers (22,300 miles) directly over the equator.

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