Back to Topic 3.2 — Structural systems
3.2.7Design Technology HL4 flashcards

Equilibrium and stability

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Card 1 of 43.2.7
3.2.7
Question

What are the two conditions for equilibrium?

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All 4 Flashcards — Equilibrium and stability

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Card 1definition

Question

What are the two conditions for equilibrium?

Answer

The forces sum to zero in every direction, and the moments sum to zero. Balanced forces alone still allow a structure to rotate.

Card 2definition

Question

What is a moment?

Answer

A force multiplied by its perpendicular distance from a pivot. Doubling the distance doubles the turning effect for the same force.

Card 3concept

Question

Name the three ways a structure leaves equilibrium.

Answer

Tipping, when the weight's line of action falls outside the support base; sliding, when a horizontal force beats friction or the fixings; and material failure, when a member yields, fractures, shears or buckles.

Card 4concept

Question

Why check stability before sizing members?

Answer

Two of the three failure modes — tipping and sliding — have nothing to do with strength, and no stronger material prevents either. Both are fixed by geometry, friction or a fixing.

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