Force system

What do we mean by the force system?

When two or more forces act on a body, they are called a force system.

Coplanar forces: The forces whose line of action lie on the same plane are known as coplanar forces.

Concurrent forces: The forces which meet at one point are known as concurrent forces.

Collinear forces: The forces whose line of action lie on the same line are known as collinear forces.

Coplanar concurrent forces: The forces whose line of action lie on the same plane and which meet at one point also are known as coplanar concurrent forces.

Coplanar non-concurrent forces: The forces whose line of action lie on the same plane but does not meet at one point are known as coplanar non-concurrent forces.

Non-coplanar concurrent forces: The forces whose line of action does not lie on the same plane but meet at one point are known as non-coplanar concurrent forces.

Non-coplanar non-concurrent forces: The forces whose line of action does not lie on the same plane and does not meet at one point also are known as non-coplanar non-concurrent forces.

Triangular law and parallelogram law of addition

What is the use of triangular & parallelogram law?

Now, we know that adding scalar quantities is very simple, just we need to add it normally but for vector quantities such as force, we cannot perform addition like this. So, to add the vector quantity we use the triangular law and parallelogram law. 

Remember that this two law can be used only for the addition of 2 force or 2 vector quantity.

Triangular law for addition: 

If two forces acting simultaneously on a body such that they can be represented by two adjacent sides of a triangle taken in same order, then their resultant will be equal to the third closing side of triangle taken in opposite direction or order.

Parallelogram law for addition:

If two vectors are represented by two adjacent sides of parallelogram then the diagonal through intersection represents their resultant.


These are the graphical method to add vector. we can also use analytical method for the addition of vector.

Scalar, vector and tensor quantity

What is scalar quantity, vector quantity & tensor quantity?

To define any scalar quantity we required only magnitude of that quantity. So, those quantity which can be fully defined based on their magnitude only are scalar quantities. eg. Time, volume, speed etc.

To define any vector quantity we required  magnitude as well as direction of that quantity. So, those quantity which can be fully defined based on their magnitude and direction are vector quantities. By knowing only the magnitude of it, it cannot be fully defined. eg. velocity, acceleration etc.

To define a tensor quantity we required magnitude, direction and the area or plane on which it is acting. So those quantity which can be fully defined only by knowing all three of these are tensor quantity. eg. Stress on a material

Dyne

What is dyne?

It is the force required to accelerate a mass of one gram at a rate of one centimeter per second squared.

1 Dyne = 1 g.cm/s^2 = 10^-5 N

Newton

What is newton?

A newton is how much force is required to make a mass of one kilogram accelerate at the rate of one meter per second square.

1N = 10^5 Dyne

1N = 1kg.m/s^2

Force

What is force?

It is the push or pull which create or tends to create motion, destroy motion or tends to destroy motion.

Force is a vector quantity.

Unit of force in SI system is Newton,
Unit of force in CGS system is Dyne.

Note: 1 N = 10^5 Dyne

Engineering Mechanics

Engineering mechanics is sub-divided into two parts:

1) Static
2) Dynamic

Here, statics deals with stationary bodies where as dynamic deals with the body in motion.

Further, dynamic can be subdivided into kinematics and kinetics.

Kinematics deals only with motion of the body and not the forces causing them where as Kinetics deals with both motion of the body and the forces causing them.

Classification of Mechanics

Engineering Mechanic can be classified as:

1) Engineering Mechanics

2) Strength of materials

3) Mechanics of fluids

Engineering mechanics deals with the rigid bodies or external force acting on the body.

Strength of material deals with the deformable bodies or internal forces acting on the bodies.

Mechanics of fluid deals with the compressible and in compressible fluid i.e. gases or liquids.

Deformable body

What do we mean by deformable body?

It is a body in which relative position of particles changes after the application of forces.

Rigid body

What do we mean by rigid body?

It is an ideal body in which relative position of particles remain same even after application of forces.

When force is applied, it only get displaced and not deformed.

Deformation does not take place here in rigid body. i.e. in rigid bodies, only displacement takes place and there is no deformation in the body.

Mechanics

What is Mechanics?

It is the science that deals with the study of forces (internal or external) and their effects on the body.