Question

Part 2A (Short Answer-2 points each) 1) What is the purpose of a Free Body Diagram? 2) What are 5 (of many) important requirements of a FBD? 3) What is the difference between an Indeterminate Structure and Determinate Structure? 4) Write the equations for Bearing Stress and Shear Stress. 5) Draw the difference between the areas used in Bearing and Shear Stress.

Answer 1

1> Purpose of FBD:

The main purpose of the free body diagram is to visualize all the forces acting on the body and concluding whether the body is in motion or in equilibrium.

2> Requirements of FBD:

To visualize all the forces remove all the contacts from the body.

To know the forces (action and reaction) acting on the body draw the vector to represent all the forces acting on the body.

Identify the individual body of interest for which you want to draw the FBD.

To know the dynamic condition direction of the acceleration or velocity should be given accordingly.

To calculate the net force.

3> Determinant structure and indeterminate structure:

A structure is said to be determinant when all the reaction forces acting on the structure can be found using all the three FBD equations. (vertical force balance equation, the horizontal force equation, and moment equation)

A structure is said to be indeterminant when all the reaction forces in the structure cannot be found using three FBD equations.

4> Bearing Stress and Shear stress:

Bearing Stress = Bearing force / characteristic area perpendicular to bearing force

Bearing Stress is the pressure at two different bodies contact and are in compression.

eg., pin in a hole under load.

Shear stress= Vertical force / Surface Area

5> Difference between Area used in bearing stress and shear stress:

in the bearing stress, the area is perpendicular to the force while in shear stress the area is parallel to force