# 8.5 Other force types

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Most of other force types have their origin in electromagnetic force.

There are scores of other forces with which we come across in our daily life. Some of these are contact, tension, spring, muscular, chemical force etc. These forces result from fundamental forces. In most of the cases, electromagnetic force is the basic force, which ultimately manifests in a particular force type.

## Operation of force

Forces differ in the manner they operate on a body. Some need physical contact, whereas others act from a distance. Besides, there are forces, which apply along the direction of attachments to the body. We can classify forces on the basis of how do they operate on a body. According to this consideration, the broad classification is as given here :

• Field force
• Contact force
• Force applied through an attachment

Forces like electromagnetic and gravitational forces act through a field and apply on a body from a distance without coming into contact. These forces are said to transmit through the field at the speed of light. These forces are, therefore, known as field forces.

Forces such as normal and friction forces arise, when two bodies come into contact. These forces are known as contact forces. They operate at the interface between two bodies and act along a line, which forms specific angle to the tangent drawn at the interface.

Besides, some of the forces are applied through flexible entities like string and spring. For example, we raise bucket from a well by applying force on the bucket through the flexible medium of a rope. The direction of the taut rope (string) determines the direction of force applied. Application of force through string provides tremendous flexibility as we can change string direction by virtue of some mechanical arrangement like pulley.

The spring force is a mechanism through which variable force (F = kx) can be applied to a body. Like string, the spring also provides for changing direction of force by changing the orientation of the spring.

## Other force types relevant to the study of dynamics

We have already discussed field forces like gravitational and electromagnetic forces in the module named "Fundamental forces". Here, we embark to study other force types, which may form the part of the study of dynamics. These are :

• Contact force
• String tension
• Spring force

## Contact force

When an object is placed on another object, two surfaces of the bodies in contact apply normal force on each other. Similarly, when we push a body over a surface, the force of friction, arising from electromagnetic attraction among molecules at the contact surface, opposes relative motion of two bodies.

In dynamics, we come across these two particular contact forces as described here.

## Normal force

When two bodies come in contact, they apply equal and opposite forces on each other in accordance with Newton’s third law of motion. As the name suggest, this "normal force" is normal to the common tangent drawn between two surfaces.

We consider here a block of mass “m” placed on the table. The weight of the block (mg) acts downward. This force tries to deform the surface of the table. The material of the table responds by applying force to counteract the force that tends to deform it.

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