Question 1

What are the three main types of internal forces in a body?

Accepted Answer

Internal forces generated within a body due to particle interaction include tension, compression, and shear. These forces exist in collinear pairs of equal magnitude but opposite directions. They cancel out between connected parts, maintaining the body's equilibrium and structural integrity.

Question 2

How does the center of gravity affect structural stability?

Accepted Answer

The center of gravity is the point where a body balances when no external force acts on it. For symmetrical bodies, it's at the geometric center; for irregular bodies, it shifts toward the heavier side. Identifying the center of gravity is critical to ensure stability and prevent tipping, especially in lifted structures.

Question 3

Why must a lifting hook be positioned directly above the center of gravity?

Accepted Answer

Placing the lifting hook directly above the center of gravity ensures balanced load distribution and prevents tipping. If the center of gravity shifts away from the centerline due to uneven loading, the structure becomes unstable. Proper hook placement maintains equilibrium and ensures safe lifting operations.

Question 4

What is the difference between internal and external forces on a body?

Accepted Answer

Internal forces arise from particle interactions within a body and cancel between connected parts. External forces, like weight, act on the body from outside and are represented by a single resultant force through the center of gravity. Understanding both is essential for analyzing conditions of equilibrium.

Question 5

How does an irregular body's center of gravity differ from a uniform body's?

Accepted Answer

A uniform or symmetrical body has its center of gravity at its geometric center. An irregular or non-uniform body has its center of gravity off-centered, shifted toward the heavier side. This difference is crucial for predicting how the body will balance and respond to external loads.

Question 6

What happens when a load becomes heavier on one side of a suspended beam?

Accepted Answer

When one side of a suspended beam becomes heavier, the center of gravity shifts away from the beam's centerline. This shift can cause instability and potential tipping. Engineers must account for load distribution and ensure the lifting hook remains positioned above the true center of gravity.

Question 7

Why are internal forces important in maintaining structural equilibrium?

Accepted Answer

Internal forces exist as collinear pairs of equal magnitude and opposite directions, canceling between all connected parts. This cancellation maintains the body's equilibrium without external intervention. Understanding internal forces is essential for designing safe structures that can withstand various loads and conditions.

内力と重心