Two Force Member and Three Force Member, Engineering Mechanics Questions and Answers

Two Force Member and Three Force Member: Identifying various types of structural members is advantageous, as each possesses distinct characteristics that significantly impact engineering analysis and design. Acquiring a clear understanding of whether a structural member belongs to the category of two-force or three-force systems can greatly simplify problem-solving processes.

Two-Force Member:

• “ A body with no force couple that is being subjected to a system of forces composed of, or reducible to, two forces acting at different points is referred to as a two-force member. ”

• For the two-force member to be in equilibrium, the two forces must have the same magnitude, the same line of action, and the opposite sense. The member's shape does not affect this fundamental requirement.

• Two-force systems are commonly encountered in engineering mechanics, especially when analyzing simple structural components or machine elements subjected to balanced loads.
• Identifying two-force members simplifies problem-solving by reducing unknowns. Knowing one force automatically determines the other force's magnitude and direction.

How to Identify Two-Force Members in a Given Structure?

• The member should be connected to other bodies at its ends using frictionless pins.
• No external force or couple should be present between the end joints of the member.
• Self-weight of a member must be negligible.

Three-Force Member:

• “ A body with no force couple that is being subjected to a system of forces composed of, or reducible to, three forces acting at three different points is referred to as a three-force member. ”

• For the three-force member to be in equilibrium, the lines of action of all three forces must be.

1. coplanar
2. and either concurrent or parallel.

Statically Determinate System:

• Any system in which the number of unknowns is equal to the number of equilibrium equations is referred to as a statically determinate system.

Note: All the problems of engineering mechanics are statically determinate.

Statically Indeterminate System:

• Any system in which the number of unknowns is greater than the number of equilibrium equations is referred to as a statically indeterminate system.

Note: Statically indeterminate problems are solved in strength of materials.