## Wednesday, 13 November 2019

We have started a new topic in our previous post i.e. engineering mechanics. We have seen there the basics of engineering mechanics such as concept of force systemprinciple of transmissibility of forces and its limitations, classification of force system and composition and resolution of forces in mechanics.

Now, we will be interested to understand here the body force and surface force in mechanics with the help of this post.

### Body force and surface force

As we have already seen that forces are acting between two bodies those are directly interacted with each other or might be at a distance away and not interacted directly.

Therefore, we can classify the forces in two types on the basis of interaction between two bodies and these are as mentioned here.
1. Body forces
2. Surface forces

### Let us first understand the body forces

Body forces act on each volume element of the body and these are exerted when the body will be kept in a gravitational, centrifugal, electric or magnetic field.

The best example of body force is the force due to gravitation and which is usually known as weight of the body.

Let us consider the example of apple falling down from its tree due to force of gravitation.

Gravitational force i.e. force of the earth on the body or object (here apple in the example) will be one good example of body force.

Briefly, we can say that body forces are the forces acting on the volume of the body.

### Example of body forces

Following are few examples for body forces which will help us to understand the basics of body forces.
1. Gravitational force
2. Centrifugal force
3. Electric field
4. Magnetic Field
5. Inertia force

### Surface forces

Surface forces act on each surface element of the body and these are exerted when the body will be kept in direct mechanical contact with another body.

The best example of surface force is the pressure force, viscus force etc.

Briefly, we can say that surface forces are the forces acting on the surface of the body.

Let us consider the following figure where a person is pulling a load, such force will be one example for surface force as there is direct mechanical contact between two bodies.

### Example of body forces

Following are few examples for surface forces which will help us to understand the basics of surface forces.
1. Pressure force
2. Viscus force
3. Frictional force
4. Normal force

Therefore, we have seen here the basics of body force and surface force with the help of this post.

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Further we will find out, in our next post, moment of force in engineering mechanics.

### Reference:

Engineering Mechanics, By Prof K. Ramesh