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# Contact Force

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 Sub Topics In general, we know that force is an influence acted on a body whether it is a pull or a push. There are many forces present in physics. Some of them are due to contact between two or more bodies. Other kind of force is like gravitational force. In which, attractive nature of the earth is revealed. Here we more concentrated on the contact forces. By the name itself it is clear that it is the force due to the bodies which are in contact with each other. According to the concept of force, contact force may also be explained as the push experienced, when two objects are pressed. The fundamental forces like gravity, electromagnetic force etc in nature are non contact forces. Contact force is nothing but the force caused by the peripheral interaction between the bodies. One example of contact force is the frictional force. Contact forces plays an important role in our day to day life.

## What is Contact Force?

Contact force is defined as the force between any two objects or a surface and an object that are in touch with each other. A contact force can be continuous or momentary. The continuous contact force is also called continuous force whereas the momentary contact is known as the impulse force.

## Contact Force Equation

Contact force equation can be represented mathematically by Newton's second law of motion. So it is given by,

F = ma
Where F is the force
m is the mass of an object
a is the acceleration of the object

We can modify this equation by multiplying with t on both sides.

So, F×t = m×a×t

F×t = mv

Where v is the velocity of the object

## Is Weight a Contact Force?

No, weight is not a contact force. It is a most common example of non contact force. We can say that, weight is a force due to the gravitational attraction of the earth on an object.

## Is Gravity a Contact Force?

No, gravity is not a contact force. Gravity is a simple force, it is due to the attraction of bodies which contain mass. In the case of gravity there is no direct contact between the object. Hence, we can say that gravity is a non contact force.

## Is Friction a Contact Force?

Yes, friction is a familiar example for contact force. It is arises due to the movement of two objects across each other. Friction is always resist the motion of objects when they are moving across each other. And it depends on the nature of the surfaces.

## Is Thrust a Contact Force?

Yes, thrust is a contact force. It is due to the contact between the air and the airplane. It is used to overcome the drag and weight of a plane.

## Is Tension a Contact Force?

Yes, tension is a contact force. It is a force which transmitted through a wire or cable when we applied a force in opposite direction. The direction of tension force is along the wire or string and it pulls equally on the opposite end of the string.

## Normal Contact Force

The normal force is a type of contact force and its component is perpendicular to the surface of contact. Consider an example, if a book is kept in a table, the surface of table exerting an upward force and weigh is in downward direction. And the normal force is acting horizontally between the two objects which are in contact.

## Types of Contact Forces

A contact force is a type of force which requires a surface or contact to accelerate an object. Contact forces are of different types. They are,
• Frictional Force : It is defined as the force exerted by a surface when it starts to move across the surface.
• Tension Force : It a kind of force which transmitted through a string or wire when it is pulled on the opposite side.
• Normal Force : It is a force which exerted on a body if it is in contact with a stationary object.
• Air Resistance : It is nothing but the frictional force between an object and air.
• Applied Force : It is a force force applied by a person on a body.
• Spring Force : It is defined as the force exerted by a stretched or compressed spring on a any particle which is attached to that spring.

## Contact and Non contact Forces

Some of the similarities and differences between contact and non contact forces as listed below:

Similarities:
1. Both contact and non contact forces can be represented by vectors
2. Both involve attraction between the objects

Differences:

 Contact Forces Non contact Forces Force arises due to the contact between two different objects Force arises due to the attraction between two objects there is no contact between the objects This force takes immediate effect after the applied force There is a time lag between the applied force and the effect of this force There is no field associated with a contact force. There is always a field associated with a non-contact force