Photomicrographs were generously provided by AlliedSignal Aerospace, Aircraft Landing Systems. We are indebted to the people at Tension Member Technology, who gave us special deals on destructive testing, and helped to analyze data. In engineering mechanics, common terms have very specific meanings. Mass is a measure of the amount of matter, closely related to the number and size of molecules. Acceleration is a measure of change in speed, or simply the effect of gravity on stationary objects.
Weight is exactly equal to force or load, commonly measured in pounds.
Stress is a measure of the load carried across some area of material. Since area is measured in units such as square inches, stress is measured in pounds per square inch. So a resting 180 pound climber puts a stress of about 1200 pounds per square inch on the rope. This type of simple stress is known as tensile stress. In rigid bodies there may be other types of stress.