Forces Static forces act on objects at rest. Compression forces shorten objects. These forces push structures. Tension forces pull objects. These forces lengthen objects.
Forces If a spring rests on a surface and weight is placed on top of the spring, it is compressed. This is an example of a compression force.
Forces If the spring is suspended in the air, like the spring of a grocery store produce scale, and weight is applied to the end of the spring, it is stretched. This is a tension force.
Forces The forces acting on a structure should be balanced.
Forces Demonstration If one person holds the ends of a slinky in each hand and stretches the slinky, a small number of coils will be evenly spaced in the middle. This section of stretched coils illustrates a beam.
Forces Demonstration If a second person applies a small amount of force on top of the stretched section of the slinky with their hand, the tops of the coils move closer together while the bottoms of the coils move further apart.
Forces Demonstration The top is under compression. The bottom is under tension. Notice the centerline of the coils. This area remains basically the same.
Properties of Materials Strength Durability Flexibility
Properties of Materials Tensile Strength ◦The amount of tension stress a material can withstand before failing. Compressive Strength ◦The amount of compression a material can withstand before failing.
Properties of Materials Durability ◦How long can a material last? Concrete and steel are very durable. Flexibility ◦Can a material bend and flex with stress? In certain designs this property could be important.