## February 11, 2009

### Overview of Chapter 4

In Chapter 4 we have seen how to solve problems involving the equilibrium of rigid bodies. The most important
thing to take away from Chapter 4 is that there is a very systematic way of approaching these problems. While it is sometimes possible to intuitively "think" your way through a problem, you are much more likely to solve a problem if you follow a systematic, step-by-step method:

• Always start by drawing a free body diagram: this is the link between the word problem and the mathematical equations that you will need to write.

• Write the equations of equilibrium: remember that you can only write three independent equations in the case of plane problems, and six independent equations in the case of three dimensional problems. In writing moment equations choose the moment point carefully, in order to minimize the number of unknowns in those equations, i.e. choose points where there are unknown forces.

• Make sure you are comfortable with the expression of forces in terms of rectangular components; either through using unit vectors, or using given angles with respect to the coordinate axes. This is often an important component in solving equilibrium problems.

Exam 1

Exam 1 covers Chapters 2-4. You are allowed to use one sheet of paper with your own notes.