If a force acting on a body of mass 1 kg produces an acceleration of 1 ms^-2, then the force is said to be 1 newton. 1 N = 1 kg ms^-2.

A small steering wheel helps to manoeuore car easily by transferring a torque to the wheels with less effort.

(i) By convention, direction of moment of a force or couple is taken as positive if the object is rotated in anti-clockwise direction.
(ii) It is negative if it rotates the object in clock wise direction.

(i) It is measured by the product of anyone of the forces (F) and the perpendicular distance between two forces (d). ፒ = F x d.
(ii) The turning effect of couple is measured by the magnitude of its moment.
(iii) Moment of the couple = Force x perpendicular distance between the force = F x S.
(iv) The unit of moment of the couple is newton meter (Nm).

(i) Torque is a vector quantity. It is acting along the direction which is perpendicular to the plane of action of force and distance.
(ii) Its SI unit is N m.
(iii) Examples : Turning a tap, winding or S unwinding a screw, spinning of a top etc.

The door can be easily opened or closed if we apply the force at a point far away from the fixed edge.
(i) In this case, the effect of the force we apply is to rotate the door about the fixed edge.
(ii) This rotational effect of the applied force is more about the 'axis of rotation' when the distance between the fixed edge and the point of application of force is more.

(i) They are classified into two types as
(a) Like parallel forces and
(b) Unlike parallel forces.
(ii) Like parallel forces: Two or more forces of equal or unequal magnitude acting along same direction parallel to each other are called like parallel forces.
(iii) Unlike parallel forces: If two or more forces act equal or unequal acting along opposite direction parallel to each other, then they are called unlike parallel forces.

(i) The system can be brought to equilibrium by applying another force which is equal to the resultant force in magnitude but opposite in direction.
(ii) Such a force is called as "Equilibrant".

(i) When several forces act simultaneously on the same object, then the combined effect of multiple forces can be represented by a single force, which is termed as resultant.
(ii) It is equal to vector sum up (adding the magnitude of forces with direction) of all the forces.

(i) The product of mass and velocity of a moving body gives the magnitude of linear momentum.
(ii) It acts in the direction of the velocity of the object.
(iii) Linear momentum = mass x velocity
p=mv

(i) When an object does not change its state during period of time, then it is said to be in the state of "rest".
(ii) When an object changes its state during a period of time, then it is said to be in the state of "motion.

(i) According to Aristotle, A moving object naturally comes to rest without any external influence or force. Such motions are termed as "natural motion".
(ii) Natural motion is an unforced motion. According to Newtonian mechanics, the natural motion is a uniform rectilinear motion, following its first law of motion. In general relatively, a natural motion may be linear or curved.

(i) It is divided into two branches, namely, statics and dynamics.
(ii) Statics: It deals with the objects which are at rest under the action of forces.
(iii) Dynamics: It is the study of moving objects under the action of forces. Dynamics is further divided as follows:
(a) Kinematics: It deals with the motion of bodies without considering the cause of motion.
(b) Kinetics: It deals with the motion of bodies considering the cause of motion.

(i) This is due to inertia of motion.
(ii) This is because velocity acquired by running is added to the velocity of the athlete at the time of jump.
(iii) Hence he can jump over a longer distance.