Engineers use particular kinds of evidence:
data from laboratory reports published by other engineers
observations and measurements of apparatus and processes inside the laboratory
observations and measurements from building models of proposed projects
observations and measurements from computer simulations and models
observations and measurements made in real-world settings
Engineers often begin the design process with computer simulations and analysis. Then they verify the simulated results with models and laboratory experiments. This process saves money for engineering firms and their clients. For example, car companies use multiple computer simulations of car crashes before they crash-test a real car.
In your classes, your projects may be “pen and paper” designs: You design and test the project on the computer or with manual calculations but do not actually build the project.
Data in engineering are quantitative; they can be counted. Depending on the nature of the problem or experiment, some data can be qualitative, described without numbers. When a structure fails or displays flaws, forensic engineers perform physical tests and sometimes collect and analyze witness testimony as they seek the causes of the problem.
For example, after a passenger airplane exploded in midair in 1996, engineers spent months reconstructing the aircraft to locate the cause. They discovered that structural problems had resulted in small vibrations. Over a long period of time, the vibrations had caused two electrical wires located near a fuel tank to rub against each other. Eventually the insulation of one of the wires had rubbed away, and the electrical current in the wire caused a spark that ignited vapors from the fuel tank. The engineers arrived at this conclusion only after painstakingly examining numerous components, sometimes in microscopic detail, ruling out many of them, focusing on the relevant ones, and ultimately performing tests in the laboratory to replicate the effects of vibrations on the wires.