The UPSC mains GS-3 paper syllabus has various subjects like Economics, Science and Technology. Science and technology in UPSC is mostly concerned with current Affairs. but it is necessary to understand the basics of science.


  • Three physical states
  • Properties of Matter
  • Inertia
  • Laws of Motion


Matter exists in three physical states:

  • Gas: It has no fixed volume or shape. It takes the volume and shape of its container, i.e., it can be compressed to fit a small container and it expands to fill a large one. For eg, oxygen, carbon dioxide and nitrogen are gases.
  • Liquid: It has definite volume but no specific shape. It assumes the shape of the portion of the container that it occupies. For eg, water, milk, oil and alcohol are liquids.
  • Solid: It has both fixed volume and fixed shape. Neither liquid nor solids are compressible to any appreciable extent. For example, iron, wood, sugar and ice are solids.

Properties of Matter

  • Every substance has a unique set of properties or characteristics that allow us to recognize it and to distinguish it from other substances. Properties of matter can be grouped into two categories:
  • Physical properties are those characteristics that can be observed without changing the basic identity of the substance, for example colour, odour, hardness, melting point, boiling point and density. Example of physical properties: Mercury is a liquid at room temperature, potassium has a melting point of 63 ᵒC, and copper metal can be drawn into thin wires.
  • Chemical properties describe the ways a substance may change or react to from other substance. Example of chemical properties: Iron metal rusts in moist atmosphere, nickel dissolves in acid to give a green solution, magnesium bums in presence of oxygen.

Change of State of Matter

The physical state of matter can be changed by changing the temperature or pressure. The process of changing:

  • (i) a solid to a liquid by heating is called melting (or fusion)
  • (ii) a liquid to a gas by heating is called boiling (or vapourisation)
  • (iii) a gas to a liquid by cooling is called condensation
  • (iv) a liquid to a solid by cooling is called Freezing


  • The property of an object by virtue of which it cannot change its state of rest or of uniform motion along a straight line its own, is called inertia. Inertia is basically a measure of mass of the body. Thus, greater is the mass, greater is its inertia and vice versa.
  • When a bus or train starts to move suddenly, the passengers sitting in it falls backward. This is due to inertia called inertia of rest.
  • When a moving train stops suddenly, the passengers sitting in it jerk in forward direction. This is due to inertia called inertia of motion.
  • We are able to protect ourselves from rains using an umbrella because rain drops cannot change their direction on their own. This is called inertia of direction.


  • Force refers to a push or pulls which tries to change the state of rest, motion, size or shape of an object. Its SI unit is Newton. 1 Newton is equal to 1 kg m/s2. There are two types of forces viz. Contact forces and Action at distance forces. Examples of Contact Forces include Frictional force, Tensional Force, Spring Force etc. The Forces in action at distance include magnetic force, electrostatic force, gravitational force etc.
  • Further, the forces which act on an object for a short interval of time but change large change in momentum is called impulsive force. Momentum is the total amount of motion present in a body. Change in Momentum is called Impulse.