# Is the Strut a Two Force Member? Why is Only One Force Used in Calculations?

• xzibition8612
In summary, the conversation discusses the concept of a two force member and its application in calculating forces in a strut. The question arises about why only one force is used in the calculations and it is explained that the other force is internal and therefore not included in the free body diagram. The conversation ends with a compliment on the expertise of the summarizer.
xzibition8612

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## The Attempt at a Solution

The book says the strut is a two force member. Why then isn't there a equal but opposite direction force Fba at point B? Isn't that what a two force member means? Why for this two-force member only the force at point A is used in the calculations? Thanks.

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hi xzibition8612!
xzibition8612 said:
The book says the strut is a two force member. Why then isn't there a equal but opposite direction force Fba at point B?

there is

but the free body diagram is for the whole thing (bed contents and strut),

so Fba is not used since it's an internal force

## 1. What is a two force member in statics?

A two force member in statics is a rigid body that is acted upon by only two forces. These two forces must be equal in magnitude, opposite in direction, and collinear.

## 2. Why is it important to identify two force members in statics?

Identifying two force members helps simplify the analysis of a structure and allows for more accurate calculations of forces and moments. It also helps identify which members are under tension and which are under compression.

## 3. How do you determine if a member is a two force member?

A member can be considered a two force member if it is supported by a pin or a roller at each end, and if it is loaded by only two forces that are acting along the line of the member.

## 4. What are some common examples of two force members?

Some common examples of two force members include truss members, cables, and ropes. These members typically have pins or rollers at each end and are loaded by two forces along the line of the member.

## 5. Can a member be a two force member if it is not loaded by two forces along the line of the member?

No, in order for a member to be considered a two force member, it must be loaded by only two forces that are collinear. If the forces are not collinear, the member will experience a moment and cannot be considered a two force member.

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