Review points from lecture 1

Forces and Equilibrium
Review points from lecture 1

Arch 324/624, Introduction to Structural Design, University of Virginia
Copyright © 1996-2009 Kirk Martini. Last Modified Wed, 07-Jan-2009 8:35

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Force Systems
- Equivalent force systems have the same resultant.
- Concurrent forces can be combined according to the parallelogram rule.
- A force can be decomposed into components using the parallelogram rule.
- Force systems which look very different may be equivalent.
- One of the primary motivations for learning to manipulate forces systems is to transform complex systems into simpler systems that are more intuitive.
- A system of forces that causes rotation is called a moment (in physics, it's called a torque.)
- A system of forces composed of two equal and opposite forces with parallel lines of action is called a couple. A couple is equivalent to a moment whose magnitude is equal to the magnitude of the force times the perpendicular distance between the lines of action.
Equilibrium
- An object is in static equilibrium when the resultant of all the forces acting on it is zero.
- For a particle in two dimensions, equilibrium means that the sum of the X components is zero and the sum of the Y components is zero, corresponding to two equations of statics.
- For a rigid body, the overall effect of a force does not change as the force is moved along its line of action.
- Applying equal and opposite forces whose lines of action are offset will cause a body to rotate.