Geometry of Deformations Equation  
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The figure shows the free body diagram of the tube near the free end B. The load on top of the tube is P which equals 30 kilo newtons directed vertically downwards. The reaction force on member 2 is F subscript 2 directed vertically downwards. The reaction force at the base of the tube is F subscript 1 directed vertically downwards.

Next, consider the overall geometry of the structure and how that geometry dictates the deformations that can occur.

Since the tube and the core are bonded together, they must deform exactly the same amount. In terms of the deformations, this relationship can be stated as:

δ1=δ2

This equation is called the geometry of deformations equation.