Question

Which statement is not correct about internal force?

Select one:

a. Internal forces describe the stress and strain inside a body, whereas external forces are applied onto the body by its surroundings.

b. Shear force acts in the axial direction of a beam and tends to make the beam grow shorter or longer.

c. Bending moment is a reaction produced by the inside of a beam when forces are applied to make it bend.

d. There are three types of internal forces in a beam -- shear force, normal force, and bending moment.

Answer 1

Answer...Option B is not correct

Explanation:-

(a) Internal forces are produced from the external forces acting on the structure such as beam, column etc.It set ups strain and stress inside a body.

Internal force includes gravity force, magnetic force ,Spring force etc.

Whereas the force which are caused by an external agent outside of the system is called external forces.

External forces include normal force, tension force, friction force etc.

So option A is correct

(b) Shear force:- It is defined as the algebraic sum of the vertical forces at any section of a beam to the right or left of the section.

It acts in transverse direction of beam and do not act in axial direction .

Shear force causes shearing deformation in the body which results in separation of a particular section. It does not cause shortening and elongation of beam .

So option B is incorrect.

(c) Bending moment:- it is defined as the algebraic sum of the moments of all the forces acting to the right or left of the section.

it is also defined as the reaction induced in the structural element when an external force and moment are applied to the element results in bending of the element.

So option C is correct

(d) There are three types of internal forces like normal force , shear force and bending moment.
Normal force - It is the force which acts perpendicular to the surface that an object contacts.

Shear force -It is the force which acts tangential to the surface of the body which causes shearing deformation.

Bending moment- It is the moment produced by external loading which tries to bend the beam in upward or downward direction.

So option D is correct.