Collection · COL-05

Engineering Oddities

Clever machines that solve small problems in surprising ways, from spinning LED 'hologram' fans to tubs that melt a city's snow, new pipes cured inside old ones, pumps that squeeze fluid through a tube, trailer floors that walk their load out, air-held domes over building sites, wire that springs back to shape when heated, farm sprinklers that strike themselves to turn, rocket test stands flooded with water, a calculator that never finishes dividing by zero, train couplers that lock on contact and the awning that shaded the Colosseum.

29 case files · 58 quiz questions · Tech, Cars, Science, Locations, Space, History, Nature

29 case files in this collection

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Free PDF: every quick fact with its ID, the write-ups, sources and a quiz with an answer key.

What Is in Engineering Oddities?

29 case files on inventions that are stranger, smaller or smarter than they look, including fan blades that paint floating pictures, the machines New York uses to melt its snow, sewer pipes relined without digging, pumps whose fluid touches nothing but a tube, trailer floors whose slats walk a load out the back, fan-held domes that keep a building site's dust inside, metal that remembers its shape, the spring-loaded arm that steps an impact sprinkler around, the water deluge under a rocket test stand, a robot that files 200 bikes under the sidewalk, a mechanical calculator, a railroad knuckle coupler and the Colosseum's velarium. Giken's ECO Cycle stores about 200 bicycles in an underground silo beneath a booth the size of a parked car. DD-009 Mahjong tiles for automatic tables contain magnets, so the machine can turn every tile face-down before stacking the walls. DD-017

The Case Files, in Order

  1. 01
    DID YOU
    KNOW?    Vertical Parking IIDD-009

    DD-009Tech

    Vertical Parking II

    This robot parks 200 bikes underground.

    Open case file →
  2. 02
    DID YOU
    KNOW?    Modern MahjongDD-017

    DD-017Tech

    Modern Mahjong

    This table shuffles and stacks the tiles for you.

    Open case file →
  3. 03
    DID YOU
    KNOW?    Footstep PowerDD-014

    DD-014Tech

    Footstep Power

    These floor tiles turn footsteps into electricity.

    Open case file →
  4. 04
    DID YOU
    KNOW?    Probe IVDD-002

    DD-002Tech+ Cars

    Probe IV

    Ford's 1983 Probe IV concept car (built with Ghia) had a drag coefficient of about 0.15.

    Open case file →
  5. 05
    DID YOU
    KNOW?    Print PrecisionDD-005

    DD-005Tech+ Science

    Print Precision

    Your printer fires drops a trillionth of a liter in size.

    Open case file →
  6. 06
    DID YOU
    KNOW?    Torque ConversionDD-075

    DD-075Cars+ Tech

    Torque Conversion

    How an automatic moves without a clutch pedal.

    Open case file →
  7. 07
    DID YOU
    KNOW?    Piston PumpsDD-072

    DD-072Tech+ Science

    Piston Pumps

    A pump whose piston never touches the fluid.

    Open case file →
  8. 08
    DID YOU
    KNOW?    Gas BlastingDD-070

    DD-070Tech+ Science

    Gas Blasting

    Breaking rock with liquid CO₂.

    Open case file →
  9. 09
    DID YOU
    KNOW?    HoloFansDD-630

    DD-630Tech+ Science

    HoloFans

    Pictures painted in midair.

    Open case file →
  10. 10
    DID YOU
    KNOW?    HoloFans IIDD-700

    DD-700Tech+ Science

    HoloFans II

    Floating figures, spinning blades.

    Open case file →
  11. 11
    DID YOU
    KNOW?    New York Hot TubDD-702

    DD-702Tech+ Locations

    New York Hot Tub

    Where city snow goes to melt.

    Open case file →
  12. 12
    DID YOU
    KNOW?    CIPPDD-676

    DD-676Tech

    CIPP

    A new pipe, no digging.

    Open case file →
  13. 13
    DID YOU
    KNOW?    Peristaltic PumpsDD-689

    DD-689Tech+ Science

    Peristaltic Pumps

    Squeeze, roll, repeat.

    Open case file →
  14. 14
    DID YOU
    KNOW?    Walking FloorsDD-665

    DD-665Tech+ Cars

    Walking Floors

    Unloading without tipping.

    Open case file →
  15. 15
    DID YOU
    KNOW?    Construction CoversDD-631

    DD-631Tech+ Locations

    Construction Covers

    A building site under a bubble.

    Open case file →
  16. 16
    DID YOU
    KNOW?    Shape MemoryDD-616

    DD-616Science+ Tech

    Shape Memory

    Bend it, heat it, it's back.

    Open case file →
  17. 17
    DID YOU
    KNOW?    Sprinkle Of TruthDD-581

    DD-581Tech

    Sprinkle Of Truth

    A sprinkler that hits itself.

    Open case file →
  18. 18
    DID YOU
    KNOW?    Deluge DaysDD-594

    DD-594Space+ Tech

    Deluge Days

    Rocket tests run on rivers of water.

    Open case file →
  19. 19
    DID YOU
    KNOW?    Vertical ParkingDD-755

    DD-755Tech

    Vertical Parking

    Part I: why Japan put its bike racks underground, and the round, quake-ready shaft that made it work.

    Open case file →
  20. 20
    DID YOU
    KNOW?    OVER 0DD-284

    DD-284Tech+ History

    OVER 0

    Ask a gear to divide by zero and it never stops.

    Open case file →
  21. 21
    DID YOU
    KNOW?    Knuckle CouplingDD-303

    DD-303Tech+ History

    Knuckle Coupling

    Push two freight cars together and they lock themselves.

    Open case file →
  22. 22
    DID YOU
    KNOW?    The ColosseumDD-121

    DD-121Locations+ History

    The Colosseum

    Rome's Colosseum had a retractable roof made of fabric.

    Open case file →
  23. 23
    DID YOU
    KNOW?    Dredging Up the...Ground?DD-323

    DD-323Tech+ Locations

    Dredging Up the...Ground?

    Dredgers suck sediment from the seabed and can build new land.

    Open case file →
  24. 24
    DID YOU
    KNOW?    A Step UpDD-341

    DD-341History+ Tech

    A Step Up

    Spiral stairs in castles helped defenders.

    Open case file →
  25. 25
    DID YOU
    KNOW?    The Googol GearsDD-327

    DD-327Tech+ Science

    The Googol Gears

    Each gear turns ten times slower than the one before it.

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  26. 26
    DID YOU
    KNOW?    Earth Movers IDD-359

    DD-359Tech

    Earth Movers I

    A Caterpillar 793F hauls about 250 short tons per load.

    Open case file →
  27. 27
    DID YOU
    KNOW?    Quarrels With Quarrying?DD-376

    DD-376Tech

    Quarrels With Quarrying?

    Marble and onyx are sliced out in clean blocks.

    Open case file →
  28. 28
    DID YOU
    KNOW?    BafflingDD-410

    DD-410Tech+ Nature

    Baffling

    Rows of concrete blocks slow water rushing down a spillway.

    Open case file →
  29. 29
    DID YOU
    KNOW?    Rolling SteelDD-423

    DD-423Tech

    Rolling Steel

    Three rollers can curl a flat steel plate into a tube.

    Open case file →

Collection Quiz

All quizzes →

58 questions from all 29 case files in Engineering Oddities. Test Your Knowledge: answers are revealed instantly.

  1. Which company makes the ECO Cycle underground bike park?

    1. Toyota
    2. Giken Ltd.
    3. Panasonic
    4. Hitachi
    Show the answer

    Answer: B. Giken Ltd. Now You Know: ECO Cycle is made by Giken Ltd. of Japan. Source: DD-009 · Vertical Parking II · Write-up · Exhibit A (Culture above ground, function underground) · Automated Parking Facility ECO Cycle (Giken Ltd., English brochure); Anti-seismic Underground Bicycle Park – ECO Cycle (JSME award summary)

  2. About how many bikes does a standard ECO Cycle hold?

    1. About 20
    2. About 200
    3. About 2,000
    4. About 20,000
    Show the answer

    Answer: B. About 200 Now You Know: The standard spec is 200 bikes; the upgraded model holds 204. Source: DD-009 · Vertical Parking II · Write-up · Exhibit B (About 200 bikes per unit) · エコサイクルの仕様 / ECO Cycle specifications (Giken Ltd.); Automated Parking Facility ECO Cycle (Giken Ltd., English brochure); Anti-seismic Underground Bicycle Park – ECO Cycle (JSME award summary)

  3. What does an automatic mahjong table use to shuffle the tiles?

    1. A rotating chamber hidden under the playing surface
    2. A robotic arm above the table
    3. Jets of compressed air
    4. Players still shuffle by hand
    Show the answer

    Answer: A. A rotating chamber hidden under the playing surface Now You Know: Tiles are churned in a chamber with a rotating floor beneath the felt. Source: DD-017 · Modern Mahjong · Write-up · Exhibit B (A spinning drum under the felt) · Automatic mahjong table (Japanese Mahjong Wiki); How does an Automatic Mahjong Table Work? A Deep Dive (The Men's Cave); US Patent 4,219,200: Device for automatically assembling tiles for the Mah-Jongg game (Izumi Takahashi, filed 1978, granted 1980)

  4. How does the machine make sure every tile ends up face-down?

    1. A camera reads each tile
    2. Magnets inside the tiles let it orient them
    3. Tiles are weighted at the bottom
    4. It doesn't; players flip them
    Show the answer

    Answer: B. Magnets inside the tiles let it orient them Now You Know: Each tile has a magnet or iron piece, so the machine's magnets can orient it face-down. Source: DD-017 · Modern Mahjong · Write-up · Exhibit C (Magnets keep tiles face-down) · Automatic mahjong table (Japanese Mahjong Wiki); How does an Automatic Mahjong Table Work? A Deep Dive (The Men's Cave); US Patent 4,219,200: Device for automatically assembling tiles for the Mah-Jongg game (Izumi Takahashi, filed 1978, granted 1980)

  5. Which Japanese station tested a 'power-generating floor' at its ticket gates?

    1. Tokyo Station
    2. Osaka Station
    3. Sapporo Station
    4. Kyoto Station
    Show the answer

    Answer: A. Tokyo Station Now You Know: JR East tested it at Tokyo Station's Yaesu North gates. Source: DD-014 · Footstep Power · Write-up · Exhibit A (Tokyo Station's power floor) · Demonstration Experiment of the 'Power-Generating Floor' at Tokyo Station (JR East press release, Jan 11, 2008); Known and unknown phenomena… in the power harvesting mat (Takefuji, NOLTA 2008); Power Generating Floor Tested at JR Tokyo Train Station (Japan for Sustainability, May 2008)

  6. What turns footsteps into electricity in JR East's floor?

    1. Solar cells
    2. Piezoelectric discs
    3. Tiny wind turbines
    4. Thermoelectric plates
    Show the answer

    Answer: B. Piezoelectric discs Now You Know: Piezoelectric elements (35 mm discs, about 600 per m²) convert pressure and vibration into voltage. Source: DD-014 · Footstep Power · Write-up · Exhibit B (Piezo discs underfoot) · Power Generating Floor Tested at JR Tokyo Train Station (Japan for Sustainability, May 2008); Demonstration Experiment of the 'Power-Generating Floor' at Tokyo Station (JR East press release, Jan 11, 2008)

  7. What was the Probe IV concept car's drag coefficient?

    1. About 0.60
    2. About 0.45
    3. About 0.30
    4. About 0.15
    Show the answer

    Answer: D. About 0.15 Now You Know: The Probe IV's drag coefficient was about 0.15. Source: DD-002 · Probe IV · Write-up · Exhibit B (Cd ≈ 0.15)

  8. In what year did Ford build the Probe IV concept?

    1. 1983
    2. 1963
    3. 1999
    4. 2008
    Show the answer

    Answer: A. 1983 Now You Know: The Probe IV was a 1983 Ford concept car. Source: DD-002 · Probe IV · Write-up · Exhibit A (1983 Ford concept)

  9. What are the two main ways inkjet printheads eject ink?

    1. Laser and toner
    2. Thermal bubbles and piezoelectric elements
    3. Magnets and springs
    4. Compressed air and vacuum
    Show the answer

    Answer: B. Thermal bubbles and piezoelectric elements Now You Know: Thermal heads boil ink into a bubble; piezo heads flex a crystal to squeeze it out. Source: DD-005 · Print Precision · Write-up · Exhibit A (Two ways to fire a drop) · Inkjet Printers: thermal and piezo ejection; FINE heads (Canon Global); Micro Piezo Inkjet Technology (Epson)

  10. How small can Epson's Micro Piezo inkjet drops be?

    1. 1.5 picoliters
    2. 1.5 milliliters
    3. 1.5 microliters
    4. 1.5 liters
    Show the answer

    Answer: A. 1.5 picoliters Now You Know: As small as 1.5 picoliters, one-and-a-half trillionths of a liter. Source: DD-005 · Print Precision · Write-up · Exhibit B (Measured in trillionths of a liter) · Micro Piezo Inkjet Technology (Epson); HP optimizes low-cost processing for inkjet printheads (Semiconductor Digest, 2008); HP offers new ink cartridge technology: 1.3 pL drops, up to 4800×1200 dpi (Philstar, 2008)

  11. Which torque converter part is driven by the engine?

    1. Turbine
    2. Impeller
    3. Stator
    4. Lock-up clutch
    Show the answer

    Answer: B. Impeller Now You Know: The impeller pumps fluid into the turbine. Source: DD-075 · Torque Conversion · Write-up · Exhibit B (Pump and turbine) · Torque converters (IEEE Technology Navigator); Zhang & Mi, Torque Converters, in Automotive Power Transmission Systems (Wiley, 2018)

  12. What does the stator do?

    1. Cools the oil
    2. Redirects returning fluid to multiply torque
    3. Shifts gears
    4. Starts the engine
    Show the answer

    Answer: B. Redirects returning fluid to multiply torque Now You Know: It turns the returning flow so it helps the impeller. Source: DD-075 · Torque Conversion · Write-up · Exhibit C (What the stator adds) · Torque Converter (IDC technical reference); Torque converter (Wikipedia)

  13. What type of pump is a piston diaphragm pump?

    1. Centrifugal
    2. Positive displacement
    3. Jet
    4. Axial-flow
    Show the answer

    Answer: B. Positive displacement Now You Know: It moves a fixed volume with each stroke. Source: DD-072 · Piston Pumps · Write-up · Exhibit A (Positive displacement) · Piston diaphragm pumps (Star Pump Alliance)

  14. In most designs, what actually flexes the diaphragm?

    1. The piston, directly
    2. Hydraulic fluid moved by the piston
    3. Compressed air
    4. The pumped liquid
    Show the answer

    Answer: B. Hydraulic fluid moved by the piston Now You Know: The piston works on a sealed hydraulic fluid. Source: DD-072 · Piston Pumps · Write-up · Exhibit B (Piston, oil, diaphragm) · Piston diaphragm pumps: technology (Emmerich GmbH); HMQ quadruplex piston diaphragm pump flyer (ABEL Pumps); How do piston diaphragm pumps work? (Universal Pumping)

  15. Where was CO₂ blasting first conceived?

    1. Wales
    2. Southern Illinois
    3. Ruhr Valley
    4. Siberia
    Show the answer

    Answer: B. Southern Illinois Now You Know: It was sold as Cardox from 1927. Source: DD-070 · Gas Blasting · Write-up · Exhibit A (Origins) · The use of carbon dioxide for dislodging coal in mines (D. R. Schooler, Missouri School of Mines thesis)

  16. What makes the liquid CO₂ burst out of the tube?

    1. A fuse of dynamite
    2. A chemical heater and rupture disc
    3. A hydraulic ram
    4. A spark plug igniting the CO₂
    Show the answer

    Answer: B. A chemical heater and rupture disc Now You Know: The disc shears at a set pressure. Source: DD-070 · Gas Blasting · Write-up · Exhibit D (The burst) · Apparatus for blasting coal, U.S. Patent 2,207,191 (Cardox Corp.); Positive phase pressure function and pressure attenuation characteristic of a liquid carbon dioxide blasting system (Energies, 2019)

  17. How many LEDs does a HYPERVSN Solo M fan carry?

    1. 672
    2. About 60
    3. About 10,000
    4. About 1 million
    Show the answer

    Answer: A. 672 Now You Know: Four rays of 168 LEDs. Source: DD-630 · HoloFans · Write-up · Exhibit B (Hundreds, not thousands) · HYPERVSN operating manual

  18. About how fast do HYPERVSN fans spin?

    1. About 670 rpm
    2. About 6 rpm
    3. About 67,000 rpm
    4. About 60 rpm
    Show the answer

    Answer: A. About 670 rpm Now You Know: About 670 revolutions per minute. Source: DD-630 · HoloFans · Write-up · Exhibit B (Hundreds, not thousands) · HYPERVSN operating manual

  19. What makes the image in a 'hologram fan'?

    1. Spinning LED strips
    2. Lasers
    3. Mirrors and smoke
    4. Water spray
    Show the answer

    Answer: A. Spinning LED strips Now You Know: LEDs on spinning blades. Source: DD-700 · HoloFans II · Write-up · Exhibit A (Painting with a spinning line) · Circuit Cellar: Build a Persistence-of-Vision Display; invidis (2018): The tech behind those furiously-spinning LED holograph-ish HYPERVSN walls

  20. Is a hologram fan a true hologram?

    1. No, it draws a flat image
    2. Yes, it's a laser hologram
    3. Yes, but only in daylight
    4. Only with 3D glasses
    Show the answer

    Answer: A. No, it draws a flat image Now You Know: It's a persistence-of-vision display. Source: DD-700 · HoloFans II · Write-up · Exhibit D (Not a real hologram) · Wikipedia: Holography; invidis (2018): The tech behind those furiously-spinning LED holograph-ish HYPERVSN walls

  21. How many snow melters did NYC run in January 2026?

    1. 2
    2. 5
    3. 8
    4. 20
    Show the answer

    Answer: C. 8 Now You Know: Eight. Source: DD-702 · New York Hot Tub · Write-up · Exhibit C (How fast) · NY1 (Jan 28, 2026): NYC rolls out snow-melting operations as cleanup continues; CBS New York: Here's how NYC is using 'hot tubs' to dig out from the winter storm

  22. How much snow can each melter handle per hour?

    1. 6-12 tons
    2. 60-120 tons
    3. 600-1,200 tons
    4. 1 ton
    Show the answer

    Answer: B. 60-120 tons Now You Know: 60 to 120 tons an hour. Source: DD-702 · New York Hot Tub · Write-up · Exhibit C (How fast) · NY1 (Jan 28, 2026): NYC rolls out snow-melting operations as cleanup continues; CBS New York: Here's how NYC is using 'hot tubs' to dig out from the winter storm

  23. What does CIPP stand for?

    1. Cured-in-place pipe
    2. Concrete-insulated plastic pipe
    3. Cast-iron pressure pipe
    4. Coated industrial polymer pipe
    Show the answer

    Answer: A. Cured-in-place pipe Now You Know: Cured-in-place pipe. Source: DD-676 · CIPP · Write-up · Exhibit A (The idea) · US EPA (2012): Retrospective Evaluation of Cured-in-Place Pipe (CIPP) Used in Municipal Gravity Sewers; Wikipedia: Cured-in-place pipe

  24. Where was CIPP first used in 1971?

    1. London
    2. New York
    3. Tokyo
    4. Berlin
    Show the answer

    Answer: A. London Now You Know: London, by Eric Wood. Source: DD-676 · CIPP · Write-up · Exhibit D (Track record) · Wikipedia: Cured-in-place pipe; US EPA (2012): Retrospective Evaluation of Cured-in-Place Pipe (CIPP) Used in Municipal Gravity Sewers

  25. What kind of pump is a peristaltic pump?

    1. Positive displacement
    2. Centrifugal
    3. Jet
    4. Axial
    Show the answer

    Answer: A. Positive displacement Now You Know: Positive displacement. Source: DD-689 · Peristaltic Pumps · Write-up · Exhibit A (How it works) · Watson-Marlow Fluid Technology Solutions: Peristaltic pumps, how do they work?

  26. What does the fluid touch in a peristaltic pump?

    1. Only the inside of the tube
    2. The rollers
    3. The motor
    4. The pump housing
    Show the answer

    Answer: A. Only the inside of the tube Now You Know: Only the tube. Source: DD-689 · Peristaltic Pumps · Write-up · Exhibit B (Tube-only contact) · Watson-Marlow Fluid Technology Solutions: Peristaltic pumps, how do they work?

  27. How does a walking-floor trailer unload?

    1. Slats walk the load out the back
    2. The trailer tips up
    3. A conveyor belt lifts it out
    4. A crane lifts it out
    Show the answer

    Answer: A. Slats walk the load out the back Now You Know: Hydraulic slats walk the load out. Source: DD-665 · Walking Floors · Write-up · Exhibit A (The slats) · Commercial Motor (Sep 1, 2005): How they work, moving-floor trailers

  28. Into how many groups are the slats usually split?

    1. Three
    2. Two
    3. Ten
    4. One
    Show the answer

    Answer: A. Three Now You Know: Three interleaved groups. Source: DD-665 · Walking Floors · Write-up · Exhibit A (The slats) · Commercial Motor (Sep 1, 2005): How they work, moving-floor trailers

  29. What holds up an air-supported construction dome?

    1. Air pressure from fans
    2. Steel columns inside
    3. Helium
    4. Wooden arches
    Show the answer

    Answer: A. Air pressure from fans Now You Know: Fans keep the inside pressure slightly higher. Source: DD-631 · Construction Covers · Write-up · Exhibit A (Held up by air) · Shenzhen Government Online: Giant 'soft pillows' reshape construction in Guangzhou and Shenzhen; CGTN (Mar 13, 2026): 9,000 m² 'giant airbag' installed at construction site in S. China

  30. What is the main reason for these domes in Chinese cities?

    1. Keeping dust and noise from neighbors
    2. Hiding the design
    3. Growing plants
    4. Storing water
    Show the answer

    Answer: A. Keeping dust and noise from neighbors Now You Know: They contain dust and noise. Source: DD-631 · Construction Covers · Write-up · Exhibit B (For the neighbors) · Shenzhen Government Online: Giant 'soft pillows' reshape construction in Guangzhou and Shenzhen; CGTN (Mar 13, 2026): 9,000 m² 'giant airbag' installed at construction site in S. China

  31. What does the 'NOL' in nitinol stand for?

    1. Naval Ordnance Laboratory
    2. Nickel Oxide Layer
    3. National Optics Lab
    4. Non-Oxidizing Liquid
    Show the answer

    Answer: A. Naval Ordnance Laboratory Now You Know: Where it was discovered. Source: DD-616 · Shape Memory · Write-up · Exhibit A (Two crystal forms) · ASME: Metal That Remembers Its Shape; Wikipedia: Nickel titanium

  32. Which phase of nitinol is easily deformed?

    1. Martensite
    2. Austenite
    3. Ferrite
    4. Plasma
    Show the answer

    Answer: A. Martensite Now You Know: The low-temperature phase. Source: DD-616 · Shape Memory · Write-up · Exhibit A (Two crystal forms) · ASME: Metal That Remembers Its Shape; Wikipedia: Nickel titanium

  33. What turns the head of an impact sprinkler?

    1. A spring-loaded arm striking the body
    2. An electric motor
    3. A wind vane
    4. A clockwork spring
    Show the answer

    Answer: A. A spring-loaded arm striking the body Now You Know: Each strike nudges it a few degrees. Source: DD-581 · Sprinkle Of Truth · Write-up · Exhibit A (Spring, spoon, strike) · Irrigation Today: The invention that changed irrigation; Google Patents: US1997901A, Water sprinkler (Englehart, 1935)

  34. Who invented the impact sprinkler?

    1. Orton Englehart
    2. Thomas Edison
    3. Clem LaFetra
    4. Henry Ford
    Show the answer

    Answer: A. Orton Englehart Now You Know: A citrus grower in Glendora, California. Source: DD-581 · Sprinkle Of Truth · Write-up · Exhibit B (A citrus grower's idea) · ASABE: Rain Bird Impact Drive Sprinkler Head, historic landmark (1990); Irrigation Today: The invention that changed irrigation

  35. Why do test-stand engines need so much cooling water?

    1. They fire in place, so exhaust keeps hitting the same spot
    2. The engines run on water
    3. To make rainbows
    4. To clean the rocket
    Show the answer

    Answer: A. They fire in place, so exhaust keeps hitting the same spot Now You Know: Without water, the flame deflector could melt. Source: DD-594 · Deluge Days · Write-up · Exhibit A (Fired in place) · NASA: NASA Stennis Completes Key Test Complex Water System Upgrade; NASA APPEL: Historic Test Stand at Stennis Points Way to the Moon (2019)

  36. How much water a minute can Stennis's B-2 stand receive?

    1. 335,000 gallons
    2. 3,350 gallons
    3. 33 million gallons
    4. 335 gallons
    Show the answer

    Answer: A. 335,000 gallons Now You Know: At 300 psi. Source: DD-594 · Deluge Days · Write-up · Exhibit B (335,000 gallons a minute) · NASA APPEL: Historic Test Stand at Stennis Points Way to the Moon (2019)

  37. How many bikes does each ECO Cycle unit store underground?

    1. About 20
    2. About 50
    3. 200 or more
    4. 2,000
    Show the answer

    Answer: C. 200 or more Now You Know: Each unit stores 200 or more bicycles in racks around a round shaft. Source: DD-755 · Vertical Parking · Slide 03 · Exhibit B (200+ bikes underground)

  38. About how long does it take to get your bike back?

    1. 13–15 seconds
    2. 1–2 minutes
    3. 5 minutes
    4. 30 seconds to 1 minute
    Show the answer

    Answer: A. 13–15 seconds Now You Know: The average wait is 13–15 seconds, even at rush hour. Source: DD-755 · Vertical Parking · Slide 06 · Exhibit E (Back in 13–15 seconds)

  39. How do mechanical calculators divide?

    1. By repeated subtraction
    2. By looking up tables
    3. With vacuum tubes
    4. By guessing
    Show the answer

    Answer: A. By repeated subtraction Now You Know: They count how many times the divisor fits. Source: DD-284 · OVER 0 · Write-up · Exhibit A (Division by subtraction) · Wikipedia: Division by zero; Wikipedia: Mechanical calculator

  40. Why does dividing by zero never finish?

    1. Subtracting zero never shrinks the number
    2. The gears overheat
    3. Zero is too large
    4. The keys stick
    Show the answer

    Answer: A. Subtracting zero never shrinks the number Now You Know: The count just keeps going. Source: DD-284 · OVER 0 · Write-up · Exhibit B (Zero never runs out) · Wikipedia: Division by zero

  41. Who patented the knuckle coupler?

    1. Eli H. Janney
    2. George Westinghouse
    3. Thomas Edison
    4. Henry Ford
    Show the answer

    Answer: A. Eli H. Janney Now You Know: The patent was issued on April 29, 1873. Source: DD-303 · Knuckle Coupling · Write-up · Exhibit A (Janney's 1873 patent) · Wikipedia: Janney coupler; Google Patents: US138405A, Improvement in car-couplings (Eli H. Janney, 1873)

  42. How does a knuckle coupler engage?

    1. It locks when cars are pushed together
    2. A worker drops a pin
    3. It's welded
    4. Magnets hold it
    Show the answer

    Answer: A. It locks when cars are pushed together Now You Know: The knuckles swing closed automatically. Source: DD-303 · Knuckle Coupling · Write-up · Exhibit B (Locks on contact) · Wikipedia: Janney coupler

  43. When was the Colosseum completed?

    1. AD 80
    2. 500 BC
    3. AD 1200
    4. AD 30
    Show the answer

    Answer: A. AD 80 Now You Know: Under Emperor Titus. Source: DD-121 · The Colosseum · Write-up · Exhibit A (Completed in AD 80) · Wikipedia: Colosseum

  44. What was the velarium?

    1. A retractable awning
    2. A water tank
    3. An elevator
    4. A gate
    Show the answer

    Answer: A. A retractable awning Now You Know: It shaded the seating. Source: DD-121 · The Colosseum · Write-up · Exhibit B (The velarium) · Wikipedia: Colosseum; Wikipedia: Velarium

  45. What do dredgers remove?

    1. Sediment
    2. Fish
    3. Ice
    4. Oil only
    Show the answer

    Answer: A. Sediment Now You Know: From the bottom. Source: DD-323 · Dredging Up the...Ground? · Write-up · Exhibit A (Purpose) · Wikipedia: Dredging

  46. Why deepen channels?

    1. For shipping
    2. For swimming
    3. For fishing only
    4. No reason
    Show the answer

    Answer: A. For shipping Now You Know: Bigger ships. Source: DD-323 · Dredging Up the...Ground? · Write-up · Exhibit B (Channels) · Wikipedia: Dredging

  47. Where were early stairs cut?

    1. Into hillsides and rock
    2. Into ice
    3. In trees
    4. In sand
    Show the answer

    Answer: A. Into hillsides and rock Now You Know: Basic steps. Source: DD-341 · A Step Up · Write-up · Exhibit A (Rock steps) · Wikipedia: Stairs

  48. What material did the Romans use?

    1. Concrete
    2. Steel
    3. Plastic
    4. Glass
    Show the answer

    Answer: A. Concrete Now You Know: And stone. Source: DD-341 · A Step Up · Write-up · Exhibit B (Romans) · Wikipedia: Stairs

  49. What is a googol?

    1. 1 followed by 100 zeros
    2. A search engine only
    3. A million
    4. A gear
    Show the answer

    Answer: A. 1 followed by 100 zeros Now You Know: 10^100. Source: DD-327 · The Googol Gears · Write-up · Exhibit A (Googol) · Wikipedia: Googol

  50. How does each gear compare?

    1. Ten times slower
    2. Ten times faster
    3. Same speed
    4. Random
    Show the answer

    Answer: A. Ten times slower Now You Know: Reduction. Source: DD-327 · The Googol Gears · Write-up · Exhibit B (Gear train) · Wikipedia: Gear train

  51. Who makes the 793F?

    1. Caterpillar
    2. Ford
    3. Tesla
    4. Volvo Cars
    Show the answer

    Answer: A. Caterpillar Now You Know: Heavy equipment. Source: DD-359 · Earth Movers I · Write-up · Exhibit A (Type) · Wikipedia: Haul truck

  52. About what payload?

    1. 250 short tons
    2. 25 tons
    3. 2,500 tons
    4. 5 tons
    Show the answer

    Answer: A. 250 short tons Now You Know: Huge. Source: DD-359 · Earth Movers I · Write-up · Exhibit B (Payload) · Wikipedia: Haul truck

  53. What cuts marble blocks?

    1. Diamond wire saws
    2. Shovels
    3. Explosives only
    4. Hands
    Show the answer

    Answer: A. Diamond wire saws Now You Know: Precision. Source: DD-376 · Quarrels With Quarrying? · Write-up · Exhibit A (Marble) · Wikipedia: Quarry

  54. What is shale used for?

    1. Cement and bricks
    2. Jewelry
    3. Glass
    4. Fuel only
    Show the answer

    Answer: A. Cement and bricks Now You Know: Construction. Source: DD-376 · Quarrels With Quarrying? · Write-up · Exhibit B (Wire saws) · Wikipedia: Wire saw

  55. What are baffle blocks made of?

    1. Concrete
    2. Wood
    3. Plastic
    4. Glass
    Show the answer

    Answer: A. Concrete Now You Know: Durable. Source: DD-410 · Baffling · Write-up · Exhibit A (Location) · Wikipedia: Baffle block

  56. Where are they used?

    1. Spillways
    2. Roofs
    3. Roads
    4. Ships
    Show the answer

    Answer: A. Spillways Now You Know: Waterways. Source: DD-410 · Baffling · Write-up · Exhibit B (Material) · Wikipedia: Baffle block

  57. How many rollers?

    1. Three
    2. One
    3. Ten
    4. Two
    Show the answer

    Answer: A. Three Now You Know: Common machine. Source: DD-423 · Rolling Steel · Write-up · Exhibit A (Purpose) · Wikipedia: Rolling (metalworking)

  58. Which roller presses?

    1. The upper
    2. The lower
    3. None
    4. Both lower
    Show the answer

    Answer: A. The upper Now You Know: Pressure. Source: DD-423 · Rolling Steel · Write-up · Exhibit B (Three rolls) · Wikipedia: Rolling (metalworking)