We have a general concept about force from our daily life experiences. When we pull or push a body, then we say a force is applied upon the body. This applied force can create or tends to create motion in a stationary body. If the body is in motion, then the applied force can cease the motion of the body or tries to increase its velocity. In both cases to apply force, it needs direct contact between the force applier and the body. These types of force are known as contact force. If the two bodies are not in direct contact, still they can apply force on each other. Such a well-known force is the force of gravitation, whose practical example is the weight of a body. When a body falls from your hand, then it quickly touches the ground. What is the reason? It happens due to the weight or attraction of the earth on the body. We define this force as the force of gravitation.
For example- the magnetic force between two poles of a magnet, the electrical force between two charged bodies, nuclear force within the nucleus. Now we will see how we can get concept about inertia and force from Newton’s first law of motion.
Newton’s first law of motion is-`Every object will continue in its state of rest or of uniform motion in a straight line unless an external force is applied to it.’
Newton’s first law expresses the property of inertia of matter.
From Newton’s first law of motion we observe that a body cannot change its state on its own. If the body is at rest, it tends to remain at rest forever and if it is in motion it tends to keep on motion with uniform speed for all time. This property of a body is termed as inertia. Thus from the Newton’s first law of motion we get the concept of inertia.
Nature of force
Contact force: We are familiar with different types of force in our daily lives. Nature of them is of different types. Some of them are produced due to direct contact between two bodies. In addition, there are some forces which do not need direct contact between two bodies. The force which needs direct contact between two bodies to be created is defined as contact force. When we push or pull a body with hand our hand exerts a force on the body at that time. This push or pull force is contact force. Since this force is the consequence of the direct contact between the hand and the body. The examples of contact forces are- frictional force, pulling force and the force created during collision. When a body tends to move or move over another body, then a resistive frictional force is produced against the motion between the contact surfaces of two bodies. Here the frictional force is produced due to direct contact between the surfaces of the two bodies. We apply pulling force on a box when we pull it over the floor. At that time frictional force is produced opposite to the motion of the box.
Non-Contact force: The force which acts without direct contact between two bodies is called non-contact force. The attractive gravitational force between two bodies, the attractive or repulsive electric force between two charged bodies, the attractive or repulsive force between two poles of two magnets, the force of attraction acting between a magnet and a magnetic material are the examples of non-contact force or distant force.