Tutorial on Engineering Design, Presentation Methods and Terminology

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"Engineering" is not the title of a typical school class, like Chemistry, Physics, Biology, or Math. Because there is confusion among students and teachers about what constitutes engineering, we provide some helpful concepts that define the field.

• Engineers are designers of objects, and of processes that get useful things done.
• Engineers build to a purpose. They research to find better or best ways to obtain that purpose.
• They employ basic understanding of physical processes.
  With math skills, they shape these understandings into formulas and equations that help predict performance.
• Engineers bring instinct and art appreciation to creativity.
• Engineers broadly search in all disciplines to find and invent in clever ways.
• The vocabulary of engineers includes well-defined and measurable quantities, and reasoning rules.

Some Important Relevant Quantities:

Energy: Transforming energy from one form to another is accomplished in many engineer-designed devices. Energy, E, has a magnitude that is measured with a unit called a Joule. The amount of energy in a process is expressed as a multiple or fraction of a Joule, the standard unit that has been adopted by agreement and years of use (by comparison, in the English system, the unit for energy is the “foot pound”). It is important to note that units can be converted from one system of measurement to another and mean the same magnitude.

Forces, Stresses, and Strains: Engineers are often concerned with the strength of things to resist forces acting on them. Objects can bend, twist, and break according to the magnitudes of forces and strengths of materials. So vocabulary is chosen to communicate these ideas.

Force, F, is a quantity that describes the strength and direction of a push or pull. It is measured in units of Newtons in the metric system (in the English system, it is the “pound”). Force is a vector, meaning that knowing its magnitude alone is not enough. You must describe the direction the force pushing or pulling, as well. In any diagram or written sentence that addresses forces, you must convey both pieces of information.

Torque, the turning force: Torque, τ (the Greek letter tau), is the amount of turning force acting, for example, on a drive shaft. A single force can produce a variety of torques. If you apply a force close to the axis, you do not get much of a turning effect. However, as you apply this same force farther away from the axis, you get a larger turning effect (that's why door handles are moved as far from the hinges as possible – an engineering choice!). Because you must know both the force applied and the distance from the axis, torque is measured in units of Newton-meters (Foot-Pound is the English unit).

Stresses and strains describe how objects are typically bent, stretched, compressed, or twisted when forces are applied. The change in shape that occurs is called the strain. Based on the shape of the object and the material it is made of, the change in shape can be anticipated. However, to know exactly what will happen, you must also know the magnitude, placement, and direction of forces applied to the object. This is called the stress. Knowing about both the force and the object, the stress and strain relationship will follow predictable rules.

Motion: When forces act on an object and are greater than forces resisting movement, the object will move according to the net force applied and until equilibrium is reached.

Velocity: This is a vector with magnitude and direction. Its units are in distance/time: For example meters/ sec. written m/s

Acceleration: This is a measure of the change in velocity in a unit of time: For example (meters/ sec ) /sec written m/s^2