Statics Notes Forces: Forces are a type of load that causes an object to translate (move linearly) in the direction of the applied force. Forces can be spread out or acting at a single location, but they always cause an object to want to translate. You can use forces to measure the intensity of one object striking another, the weight of a car as it drives across a bridge deck, or the effect of water pressure on the side of a submarine. Flip to Chapters 9 and 10 for more on forces. I Moments: Moments are a type of load that causes an object to rotate in space without translation. Moments are usually the result of some sort of twisting or spinning effect, such as a shaft attached to a motor, or a reaction from a second object that is acting on the other. For example, turning the handle of a wrench applies a moment to a bolt, which then causes it to rotate. Chapter 12 gives you the lowdown on moments. Concentrated forces: Concentrated forces (or forces that act at a single point) include the force from a ball as it's thrown toward a wall, or even the force that your shoes exert on the floor from your self weight. I cover these forces more in Chapter 9. Distributed forces: Distributed forces are forces that are spread over an area and are used to represent a wide variety of forces on objects. The weight of snow on the roof of your house or of soil pressure on your basement wall is a distributed load. Chapter 10 shows you how to deter- mine their net effect (or the resultant), and Chapter 11 illustrates how to determine the location where this resultant is acting. V Concentrated moments: Concentrated moments are a type of load that causes a rotation effect on an object. The behavior of your hand on a door knob or a wrench on a nut is an example of rotational behaviors that are caused by moments. I describe the types of moments and how they are created in more detail in Chapter 12. For example, suppose that I rest a ladder on the ground at location Point 1 and on a ledge at location Point 2 (as shown in Figure 2-1) and want to define the properties of the line that connects these two points (the slope). 2 y 10 ft = Rise 1 × - 20 ft = Run slope = m = Ay _ y2-y1 _rise _10-0 _ 1 _ 05 Ax X2 -X1 run 20-0 2
The sum of the interior angles for a polygon having n sides can be given by the expression Total Degrees in Polygon = 180(n-2) You can easily confirm this formula by using your basic knowledge of tri- angles and quadrilaterals. A triangle has three sides (n = 3) and a total of 180 degrees: 180(3 - 2) = 180(1) = 180. Similarly, a quadrilateral has four sides (n = 4)