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Stuff Every Engineer Should Know

Units, forces, materials, circuits, fluids, heat and design: the core ideas every engineer works with.

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  1. How many base units does the International System of Units (SI) have?
    Show the answer

    7. The SI rests on 7 base units. Every other unit, like the newton or the volt, is built by multiplying and dividing those seven.

  2. Since the SI redefinition voted in 2018, what defines the kilogram?
    Show the answer

    The Planck constant, a constant of nature. For over a century the kilogram was one metal cylinder, Le Grand K. Now it is tied to the Planck constant, so any well-equipped lab can realize it without visiting the cylinder.

  3. In today's SI, how precisely is the value of the Planck constant known?
    Show the answer

    Exactly, because the SI fixes its value. The revised SI turns the logic around. Seven constants of nature get exact fixed values, and the units are defined from them. So h has no measurement uncertainty any more.

All 166 practice questions

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  1. How many base units does the International System of Units (SI) have?
  2. Since the SI redefinition voted in 2018, what defines the kilogram?
  3. In today's SI, how precisely is the value of the Planck constant known?
  4. One newton of force equals which combination of SI base units?
  5. One joule of work is the same as what?
  6. A watt measures power. What is one watt equal to?
  7. The pascal, the SI unit of pressure and stress, equals what?
  8. In SI symbols, how is MW different from mW?
  9. What factor does the SI prefix micro (symbol μ) stand for?
  10. How many significant figures are in the measurement 0.00450 m?
  11. A scale gives 5.21, 5.22 and 5.21 kg for a true 6.00 kg mass. The readings are:
  12. In measurement standards, what is a tolerance?
  13. Mars Climate Orbiter was lost in 1999 because software mixed up which units?
  14. About how many newtons are in one pound-force?
  15. A 5.0 kg wrench is taken to the Moon. What happens to it?
  16. In the US British Gravitational system used in statics, what is the unit of mass?
  17. For an object at rest, Newton's second law F = ma becomes what?
  18. What does a free-body diagram show?
  19. A force's line of action passes right through the pivot. What moment does it make about that pivot?
  20. Torque is force times lever arm. Which SI unit is correct for torque?
  21. When solving a static equilibrium problem, where are you allowed to sum moments?
  22. For most material pairs, how does the static friction coefficient compare to the kinetic one?
  23. In the basic dry friction model, does a wider contact area increase the friction force?
  24. About what is the static friction coefficient for rubber on dry concrete?
  25. In mechanics of materials, what is stress?
  26. A 2 m bar stretches 1 mm. What are the units of its strain?
  27. Steel's Young's modulus is about 200 GPa. Aluminum's is about how much?
  28. In Hooke's law, F = -kx, what are the SI units of the spring constant k?
  29. What happens when a metal part is loaded past its elastic limit and then unloaded?
  30. NASA's structural standard sets what minimum ultimate design factor for metallic spaceflight structures?
  31. A beam rests on two supports with a load in the middle. Which side is in tension?
  32. In a homogeneous beam under simple bending, where is normal bending stress zero?
  33. Why is an I-beam shaped like an I?
  34. A 1/8 inch thick, 1 inch tall ruler is bent on edge instead of flat. How much stiffer is it?
  35. Why are bridge and roof trusses built from triangles?
  36. In an ideal pin-jointed truss, what kind of force does each member carry?
  37. If a slender pinned column is made half as long, its critical buckling load:
  38. How can metal fatigue break a part that never sees a load above its yield strength?
  39. Which metal typically has a fatigue endurance limit below which fatigue failure is not expected?
  40. How is the mechanical advantage (MA) of a simple machine defined?
  41. For an ideal pulley system, the mechanical advantage is roughly equal to what?
  42. A 12-tooth motor gear drives a 36-tooth wheel gear. Ideally, what happens to the output torque?
  43. Which typically converts input energy into useful work most efficiently?
  44. Which common structural metal is stiffest for the same cross-sectional shape?
  45. Which is least dense: aluminum, titanium, or iron?
  46. Why is titanium attractive for demanding structures and implants?
  47. What separates ductile behavior from brittle behavior before fracture?
  48. What does a material's yield strength mark?
  49. What is ultimate tensile strength on an engineering stress-strain curve?
  50. Which property describes resistance to indentation, scratching, and local plastic deformation?
  51. In materials engineering, what is corrosion?
  52. What combination can create galvanic corrosion?
  53. Is ordinary concrete generally stronger in compression or tension?
  54. Why are steel reinforcing bars placed in concrete members?
  55. In a unidirectional fiber composite, where is stiffness and strength greatest?
  56. Which polymer class can usually be softened, reshaped, and reprocessed by heating?
  57. Why can a cured thermoset not simply be melted and remolded?
  58. What tradeoff often follows faster quenching of steel?
  59. Why is quenched steel often tempered afterward?
  60. What is a common purpose of annealing a metal?
  61. Why can welding distort a metal assembly even after it cools?
  62. What makes machining a subtractive manufacturing process?
  63. Which process shapes a metal by pouring it molten into a mold?
  64. Which process shapes heated solid metal through repeated deformation?
  65. What defining action makes a process additive manufacturing?
  66. What does computer numerical control do in a machine tool?
  67. What is the main purpose of geometric dimensioning and tolerancing?
  68. For a uniform bar, what commonly happens to its length as temperature rises?
  69. Why do long bridges use expansion joints?
  70. Which load category includes a structure's own permanent weight?
  71. Which load category includes occupants and movable furniture?
  72. How can wind load act on building surfaces?
  73. Why does a heavier structure generally develop more earthquake inertia force at the same acceleration?
  74. When weak near-surface soil cannot support a heavy structure, what foundation may be needed?
  75. What major horizontal action must a retaining wall resist?
  76. Why is drainage placed behind many retaining walls?
  77. Which bridge type uses horizontal beams carried by vertical supports?
  78. How does an arch bridge mainly carry its load to the supports?
  79. In which bridge type do inclined cables connect the deck directly to towers?
  80. Which bridge hangs its roadway from main cables that pass over towers?
  81. What central lesson did the first Tacoma Narrows Bridge failure teach designers?
  82. Why is a straight road surface often crowned or cross-sloped?
  83. Why is the outside edge of a road curve often raised?
  84. Kirchhoff's junction rule (current law) is a direct result of which conservation law?
  85. Around any closed loop in a circuit, what do all the voltage rises and drops add up to?
  86. A US wall outlet is called 120 V AC. About what peak voltage does it actually swing to?
  87. Why do power companies send electricity across the country at very high voltage?
  88. An ideal transformer has 10 times more secondary turns than primary turns. What does it do to voltage?
  89. After the switching transient, what does steady DC on a transformer's primary produce at its secondary?
  90. A 100 amp-hour battery is discharged at a 1C rate. What current is that?
  91. A battery's specific energy is in Wh/kg. What does its specific power in W/kg tell you?
  92. A GFCI outlet trips when the current going out and coming back differ by about how much?
  93. Which shock can a GFCI NOT protect you from?
  94. Changing magnetic flux passes through a coil. What happens to induced voltage if you double the turns?
  95. By Lenz's law, the current induced by a changing magnetic flux does what?
  96. When does a simple DC motor connected directly to fixed voltage draw the most current?
  97. In a basic rotating electromagnetic machine, how does motor construction differ from generator construction?
  98. As AC frequency goes up, what happens to an inductor's opposition to current (its reactance)?
  99. After it charges, how does a capacitor behave in a steady DC circuit?
  100. In an AC circuit with only a capacitor, how are current and voltage timed?
  101. An empty capacitor charges through a resistor. About how full is it after one time constant (RC)?
  102. What happens to the resistance of a copper wire as it gets hotter?
  103. Which metal has the lowest electrical resistivity at room temperature?
  104. In its superconducting state, what is a material's DC electrical resistance?
  105. In a copper wire, how does the direction of conventional current compare to electron flow?
  106. In typical household copper wiring, how fast do electrons drift compared with the electrical signal?
  107. Since the 2019 SI redefinition, the ampere is defined by fixing the value of what?
  108. North America's grid runs at 60 Hz. What frequency does Europe's grid use?
  109. If electricity use suddenly exceeds generation on a grid, what happens to the grid frequency?
  110. In three-phase power, how far apart in phase are the three voltages?
  111. In 1975, Gordon Moore revised his famous prediction. How often did he then say chip density would double?
  112. The first working transistor, built at Bell Labs in December 1947, was made from which semiconductor?
  113. Jack Kilby demonstrated the first working integrated circuit in 1958 at which company?
  114. In MOSFET, what do the letters M, O and S stand for?
  115. Why did CMOS, which pairs n-channel and p-channel transistors, become the dominant chip technology?
  116. About how many transistors were on Intel's first microprocessor, the 4-bit 4004 from 1971?
  117. Why did silicon replace germanium as the main transistor material?
  118. Which single type of logic gate can be combined to build any Boolean function at all?
  119. To capture sound up to 20,000 Hz digitally, the sampling rate must be more than what?
  120. What happens to a frequency above the Nyquist frequency when it is sampled?
  121. An EV turns over 77 percent of grid energy into power at the wheels. What about a gasoline car?
  122. AC won the 1890s War of the Currents. What is high voltage DC (HVDC) used for today?
  123. In a working battery, what travels through the electrolyte inside the cell?
  124. Discharge a battery at a much higher C-rate. What happens to the amp-hours you get out?
  125. A battery discharge to at least what depth of discharge counts as a deep discharge?
  126. In EIA's 2010 US manufacturing survey, machine drives used about what share of delivered electricity?
  127. What physical ratio defines pressure on a surface?
  128. For a constant-density liquid, how does pressure change with depth h?
  129. What does Pascal's principle say an enclosed fluid transmits undiminished?
  130. An ideal hydraulic output piston has five times the input area. How does output force compare?
  131. According to Archimedes' principle, what equals an object's buoyant force?
  132. When will an object float in a surrounding fluid?
  133. In steady incompressible flow, what happens to speed where a pipe narrows?
  134. Along a level Bernoulli streamline, what accompanies a higher fluid speed?
  135. Which assumptions underlie the simple Bernoulli equation along a streamline?
  136. For flow in a smooth tube, which Reynolds number is clearly in the turbulent range?
  137. What distinguishes turbulent flow from laminar flow?
  138. What property measures a fluid's resistance to shearing flow?
  139. In laminar Poiseuille flow, how does tube radius affect flow rate?
  140. How does a centrifugal pump raise a fluid's pressure?
  141. What chiefly sets an ideal positive-displacement pump's flow rate?
  142. What initiates cavitation inside a pump?
  143. Which heat-transfer mode moves energy through direct physical contact?
  144. Which heat-transfer mode requires bulk motion of a fluid?
  145. Which heat-transfer mode can cross a vacuum?
  146. What does insulation R-value measure?
  147. If A is in thermal equilibrium with B and with C, what does the zeroth law say about B and C?
  148. With work W defined as done by a system, what is its internal-energy change?
  149. What heat flow cannot occur spontaneously under the second law?
  150. What limit does the third law place on cooling?
  151. How is a heat engine's thermal efficiency defined?
  152. What is the maximum ideal efficiency between reservoirs at Th and Tc?
  153. How is a heating heat pump's coefficient of performance defined?
  154. Where does refrigerant absorb heat in a household refrigerator?
  155. What is the correct order of a four-stroke engine cycle?
  156. What makes a control system closed-loop?
  157. In feedback control, what is the setpoint?
  158. What information do the P, I, and D terms use?
  159. Why is engineering design usually iterative rather than a straight line?
  160. Which test question is validation meant to answer?
  161. What does a failure mode and effects analysis do before failures occur?
  162. Why can two redundant components still fail together?
  163. What does the first NSPE fundamental canon put above other engineering interests?
  164. What technical sensitivity did the Challenger investigation identify in the solid rocket motor joint?
  165. In the built Hyatt Regency walkway system, what supported the second-floor walkway?
  166. Which wind direction exposed the overlooked Citicorp Center structural weakness?