The UPSC mains GS3 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.
TOPICS
 Gravitation
GRAVITATION
What is Gravitational Force?
 Each body in this universe attracts other bodies towards itself with a force known as Gravitational Force, thus gravitation is a study of the interaction between two masses. Out of the two masses, the heavier one is called source mass and the lighter one is called test mass.
 Gravitational force is a central force which depends only on the position of test mass from the source mass and always acts along the line joining the centres of the two masses.
Newton’s Law of Gravitation
 According to Newton’s law of gravitation, every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
Mathematically it can be represented as,
F = Gm1m2/r2
Where,
 F is the Gravitational force between two objects measured in Newton (N).
 G is the Universal Gravitational Constant with a value of 6.674 × 1011 Nm2kg2.
 m1 is the mass of one massive body measured in kg.
 m2 is the mass of another massive body measured in kg.
 r is the separation between them measured in kilometre (Km).
 In SI units: 6.67 × 1011 Nm2 kg2, In CGS units: 6.67×108 dyne cm2 g2
Density and Specific Gravity
Difference Between Density and Specific Gravity 

Density 
Specific Gravity (Relative Density) 
It is the mass of an object per unit volume  Relative density is the ratio of a substance’s weight to the weight of the same volume of water. 
To calculate density, we need to know the weight and volume of the substance.  We can get this by dividing the density of a substance with the density of water. 
It is represented in absolute term  It is represented in relative term 
Its symbol is ρ is represented in kilogram per cubic meter  It does not have a SI unit 
It is used in many domestic and commercial applications  It is used in industries to measure the concentration of solutions. 