Mechanical Systems Fundamentals
Core concepts
Mechanical systems fundamentals underpin every other domain, so expect questions that test whether you can reason from first principles rather than recall a datasheet. You must be fluent in force, torque, work, power, and energy relationships; the difference between static and dynamic loading; stress and strain, elastic limit, and fatigue failure; and the behavior of simple machines such as levers, gears, belts, and pulleys. Understand mechanical advantage, gear ratios, and how speed and torque trade off through a drive train. Know the basics of bearings, lubrication regimes, alignment, and vibration as indicators of machine condition.
Traps to watch
A common trap is confusing mass with weight or mixing units between SI and imperial. Another is assuming power scales linearly with speed when torque is constant versus when torque falls with speed. Questions on gear trains often hide a direction-of-rotation twist. Fatigue questions may tempt you to pick yield strength as the design limit when the correct answer is endurance or fatigue strength under cyclic loading. Watch for questions that describe a system in equilibrium but ask about internal forces.
Worked example
A motor delivers 15 kW at 1450 rpm. Torque T = P/ω, where ω = 2πN/60 = 2π(1450)/60 ≈ 151.8 rad/s. So T ≈ 15000/151.8 ≈ 98.8 N·m. If a gearbox with a 4:1 reduction is added, output speed falls to about 362 rpm and output torque rises to roughly 395 N·m, ignoring losses. Rule of thumb: in an ideal reducer, speed falls and torque rises by the same ratio, and power stays constant.