Applied Mechanics (General Engineering) (SSC JE)

The branch of physical science that deals with the state of rest or state of motion of a body under the action of certain forces is known as engineering mechanics.

Strain–It represents change in dimension to its original dimension. It is dimensionless parameter.
• Stress–Internal resisting force per unit area is called as stress.
• Moment of inertia (2nd moment of area)– Moment of inertia is a quantity which expresses the body's tendency to resist external angular acceleration, which can calculated as the sum of the products of the mass of the each particle of the body with the square of its distance from the axis along which it is to be rotated.

Malleability–The ability of a material to be beaten into sheet is called as malleability. Ductility–The ability of a material to be deformed easily without being fractured. Toughness–The ability to resist impact loading is called as toughness.
Hardness–The ability of material to resist the surface deformation.

Torque–A vector quantity which has the tendency of a force to cause or change the rotational motion of a body. It is also called as moment of force.

Frictional force acts in the direction opposite of motion. It is non-conservative force and depends on the angle and position of the object.
µ = tan θ
where,
µ = coefficient of friction
θ = angle of inclination

Impulse–The product of force (F) and time (t) is called as impulse that represents the time interval in which a large amount of force acts on a body.

In order to determine the effects of force, acting on body, we must know the following characteristic of a force–
1. The magnitude of the force
2. The line of action of the force
3. The nature of the force i.e. push or pull.
4. The point at which the force is acting.
A force while acting on a body may–
(a) Change the motion of a body
(b) Retard the motion of a body
(c) Balance the forces already acting on a body and
(d) Give rise to the internal stresses in a body.

Concurrent forces are those forces whose lines of action meet at one point
• Coplanar forces are those forces whose lines of action lie on the same plane. If the lines of action of the force lie in the same plane and they meet at a point those
forces are called coplanar concurrent forces.
• Collinear forces are those forces whose lines of action lie on the same line.

• The dimension of the moment of a force and angular moment are not is same in the given dimensions.