Mechanical engineering and degrees of the like are some of the most in-demand skill sets for new graduates. There are certain mechanical and physical principles that every mechanical engineer needs to understand like the back of their hand if they want to excel in their career path. If you find yourself knowing all of these principles already, then you’re probably pretty good at your job.

# Clearances and Tolerances

When designing any number of complex and precise parts, keeping in mind clearances and tolerances is key. A tolerance in engineering terms is usually defined as the permissible limit or limits of variation of a part. This becomes important when you are ordering parts like nuts and bolts or trying to determine which manufacturing process to use to create your design. Certain machines will have a maximum tolerance and if you need a tighter tolerance, then you need to find a new machine. Clearances naturally come out of tolerances. For example, you might know you must maintain a clearance of 2 cm + or – .1 cm. This clearance would likely be there to avoid friction or to avoid the part catching another moving part. The tolerance of this clearance value would be the .1 cm. All make sense?

# Force, Pressure, and Friction

May the force, pressure, and friction be with you. Forces are the measure of mass times acceleration. They are what determine our everyday life. Friction and pressure are both types of forces, often the most discussed. Focusing in on the latter, friction is the reason everything works the way it does. Without it, we would all slide around endlessly like in a real life pinball machine. Friction is a resisting force exerted on an object when in contact with another object. There is kinetic and static friction, which each usually have a different coefficient for a given surface. Essentially, friction is a resisting force that can be variable based on surface properties, velocities, and accelerations. Pressure is similar to friction in that it is a continuous force exerted against an object when something is in contact with it. It is also given as a force on a specified area, think pounds per square foot (psi).

# Velocity and Acceleration

Velocity is the speed of something in a given direction. Velocity is generally a vector of sorts, meaning that it has both a numerical speed value and a directional value. Acceleration, on the other hand, is the change in velocity in a given time. In terms of physics, there can be both positive and negative acceleration, negative often being called deceleration. Understanding these two concepts of velocity and acceleration are foundational to life as an engineer. Every other principle, like work, energy, forces… everything, build off of your understanding of these concepts.

# Work and Energy

Work builds off of the principles of force. If work is done on an object, a force is applied to that object to move it a certain distance in a certain direction. Energy is the capacity of doing work. For example, when you are in a car at the top of a roller coaster. You have a certain amount of energy, or potential, to fall down the track and gain speed. As you begin to fall, your potential, or energy, begins to decrease as the force of gravity begins doing work on you. Think of energy as the currency to do work. Your manager pays you in energy and you in turn work all day. Remember, that’s just an analogy, we don’t get paid in red bulls – at least I don’t. These principles aren’t hard if you understand forces and ultimately accelerations, but like everything in physics, it all builds on the previous principles.

# Stress and Strain

Stress is the force per unit area and strain is the deviation or change in shape as a result of stress. In other words, stress is the number of tests you have coming up when you are in college, and strain is how little free time you then have in your schedule. These concepts become really important in material sciences. Their values will change for different materials, often referred to as maximum stress and strain for a given material. Exceeding these maximum values often result in deformation or part failure.

All of these concepts were physical in nature, and they involve a lot of math too. Many mechanical engineers use these principles on a daily basis, although not always in way you use them in physics class in college. Most CAD programs and other computer tools will take the complexity out of the calculation and determine all of these values automatically. That doesn’t mean you don’t have to understand the principles, but it does make the job of the mechanical engineer just a little bit easier.

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