10.2 THE BASIC EQUATIONS OF STATICS

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There are two basic balances that must exist in any statics problems.

if the sum of the forces is not zero, then the system will undergo translation, and the problem cannot be solved with statics methods.

if the sum of moments is not zero, then the system will undergo rotation, and the problem cannot be solved with statics methods.

At least one of these two equations will appear in every statics problem.

A simple example,

Let's consider a force balance problem, ([Hibbeler, 1992]prob 3-40, pg. )

10.2.1 Practice Problems

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1. Two cables (AB and AC) and a force (P) act on the top of a flag pole (AD). Find the magnitude of force P required to keep the flag pole standing? Assume that cable AB is under 5 KN of tension.

ANS

2. The 500 lb pendulum below is hung from beam ABC with three cables (BD, DC and DE). The cables are joined at D with a ring. What is the tension in each of the cables? (25%)

3. F1 is a projected vector with a magnitude of 15KN, the magnitude of F2 is 10KN. F2 is represented with direction cosines, and lies in the negative `x' direction. Find the resultant of these vectors in cartesian vector notation. (50%)

10.2.2 References

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Hibbeler, R.C., Engineering Mechanics: Statics and Dynamics, 6th edition, MacMillan Publishing Co., New York, USA, 1992.