• The relation between motion and force is given by Newton’s three laws of motion.

• The first law of motion defines force as something which acting on a body changes its state of rest or of uniform motion along a straight line. It also defines inertia which is a property common to all bodies.

• The mass of a body is the measure of its inertia.

• The second law gives relationship between change in motion and force.

• The third law of motion tells that forces always exist in pairs and they act on two different points or bodies.

• Friction comes in existence at the interface of two bodies due to their relative motion and always impedes the motion. It is useful as well as harmful in many of our activities.

• Bodies attract each other due to force of gravitation and the constant of proportionality G is a universal constant. Its value is 6.67 x 10-11 Nm2 kg-2.

• Weight of a body is the force with which Earth attracts a body, stationary with respect to the Earth.

• Mass of a body remains same everywhere but weight changes.

• The acceleration with which bodies fall towards earth is called acceleration due to gravity ‘g’. Its value at the equator is 9.8 ms-2. It also changes from place to place and with height or depth.

• Weightlessness is a state in which the body exerts no force on its base and the system has a free fall acceleration i.e. equal to acceleration due to gravity.

• The total force exerted by a fluid on any surface in its contact is called thrust.

• The thrust per unit surface area is known as pressure.

• Archimedes principle states that there is an apparent loss in weight of a body when it is wholly or partially immersed in a fluid. The loss in weight is equal to the weight of fluid displaced.