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1. Force:

(i) Force generally denotes push or pull.

(ii) Force can (a) produce motion, (b) stop motion, (c) change the direction of motion, (d) change the dimension, in a body.

(iii) Force is defined as an external agent which changes or tends to change the state of rest or uniform motion of a body or changes the direction of the body or deforms the body.

2. First Law of Motion:

(i) The First Law of Motion states that an object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force.

(ii) The tendency of undisturbed objects to stay at rest or to keep moving with the same velocity is called inertia. The First Law is also known as the Law of Inertia.

(iii) While travelling in a motorcar, with the application of brakes, the car slows down but our body tends to continue in the same state of motion because of its inertia of motion.

(iv) When we are standing in a bus and the bus begins to move suddenly, we tend to fall back because of the inertia of rest.

(v) When a motorcar makes a sharp turn at a high speed, we tend to get thrown to one side. This is due to the inertia of direction. 

(vi) Mass of a body is the measure of its inertia, i.e., the more the mass of a body, the more is the inertia.

3. Second Law of Motion:

(i) Momentum p is defined as the product of mass m and velocity v. It is formulated as p=mv.

(ii) Momentum has both direction and magnitude. Its direction is the same as that of velocity. The SI unit of momentum is kilogram-metre per second kg m s-1. 

(iii) The Second Law of Motion states that the rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force.

(iv) According to Newton's Second Law, F= ma. Where F, m and a are force, mass and acceleration of the mass caused by the force.

(v) The SI unit of force is newton N and is defined as the force that produces an acceleration of 1 m s-2 in an object of 1 kg mass.

(vi) Impulse of force is product of very large force acting on a body and the very short time interval for which force acting.

Impulse=Force×time

(vii) Impulse can also be calculated as the difference between final momentum to initial momentum.

4. Third Law of Motion:

(i) The Third Law of motion states that when one object exerts a force on another object (action), the second object instantaneously exerts a force (reaction) back on the first. These two forces are always equal in magnitude but opposite in direction. These forces act on different objects and never on the same object.

(ii) Even though the action and reaction forces are always equal in magnitude, these forces may not produce accelerations of equal magnitudes. This is because each force acts on a different object that may have a different mass.

5. Conservation of Momentum:

(i) According to the Law of conservation of momentum, in a given system, the sum total of momentum is a constant quantity, provided no external force acts on the system.

(ii) In case of collision between two objects, Law of conservation of momentum states that the sum of momenta of the two objects before the collision is equal to the sum of momenta after the collision provided there is no external unbalanced force acting on them.

Opposite directions with equal velocities.

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Opposite directions with unequal velocities.

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Opposite directions with equal or unequal velocities.

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Same direction with equal velocities.

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