A pull or push which changes or tends to change the state of rest or of uniform motion or direction of
motion of any object is called force. Force is the interaction between the object and the source (providing
the pull or push). It is a vector quantity
All the forces observed in nature such as muscular force, tension, reaction, friction, elastic, weight,
electric, magnetic, nuclear, etc., can be explained in terms of only following four basic interactions
Force which acts on an object at a distance by the interaction of the object with the field produced by
other object is called field force. Examples
Tension in a string is a electromagnetic force. It arises when a string is pulled. If a massless
string is not pulled, tension in it is zero. A string suspended by rigid support is pulled by
It is the component of contact force tangential to the surface
To every action, there is always an equal and opposite reaction. Newton’s law from an 1803
translation from Latin as Newton wrote
Two or more than two objects which interact with each other form a system
A free body diagram consists of a diagrammatic representations of a single body or a subsystem
Each body continues to be in its state of rest or of uniform motion in a straight line unless
compelled by some external force to act otherwise.
The rate of change of momentum of a body is proportional to the applied force and takes place in the
direction in which the force acts.
(a) The Second Law is obviously consistent with the First Law as F = 0 Implies a = 0.
(b) The Second Law of motion is a vector law. It is actually a combination of three equations, one for
each component of the vectors :
When objects are in equilibrium
To solve problems involving objects in equilibrium:
Every spring resists any attempt to change its length; when it is compressed
or extended, it exerts force at its ends
It does not measure the weight. ?t measures the force exerted by
the object at the hook.
When two objects are connected through a string and if the string have the following properties :
(a) The length of the string remains constant i.e. inextensible string.
(i) There is a regular contact between two objects.
(ii) Objects are rigid.
NEWTON’S LAW FOR A SYSTEM
Fext ? m1a1 ?m2a2 ?m3a3 ?......
Net sum of real and pseudo force is taken in the resultant force.
a Acceleration of the particle in the non inertial frame