Collection · COL-09

Everyday Physics

Wine tears, inkjet drops, a blue glow that outruns light in water, a street that fools your balance, paint held on by static, the fluid inside an automatic car, water that carries a current, a laser that branches in a soap film, a golf ball that squashes and springs back, a crane kept upright by its counterweights, sunscreen that goes dark on a UV camera, vapor trails left by radiation, rainbows that are really circles, iron too hot for a magnet, beads that fall into a bell curve, metal that sparks in a microwave, a desk toy that passes momentum down the line, plasma made in a microwave, the ball in a ballpoint pen, water that holds itself together, a match head catching fire, a camera that bends propellers, charges that link up into lightning, plasma, the fourth state of matter,, the quartz crystal that keeps your watch on time and the metals that color fireworks.

34 case files · 68 quiz questions · Science, Tech, Locations, Cars, History, Nature, Space

34 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 Everyday Physics?

34 case files on physics you can see or feel: in a wine glass, a printer, a reactor pool, a tilted street, a paint booth, a car's automatic transmission, water carrying a current, a soap film, a golf ball at impact, a crane's counterweights, a UV camera, a cloud chamber, a rainbow, a red-hot piece of iron, a Galton board, a microwave oven, a Newton's cradle, a ballpoint pen, a drop of water, a match, a phone camera and a thunderstorm. In the Marangoni effect, liquid flows from regions of low surface tension toward regions of high surface tension. It's why wine forms 'tears' on the glass. DD-024 The blue glow in nuclear reactor pools is Cherenkov radiation: electrons moving faster than light travels in water (about 75% of c). DD-020

The Case Files, in Order

  1. 01
    DID YOU
    KNOW?    Marangoni MotionDD-024

    DD-024Science+ Tech

    Marangoni Motion

    Surface tension can make liquid pull itself across a surface.

    Open case file →
  2. 02
    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 →
  3. 03
    DID YOU
    KNOW?    Cherenkov GlowDD-020

    DD-020Science+ Tech

    Cherenkov Glow

    This blue glow is particles outrunning light in water.

    Open case file →
  4. 04
    DID YOU
    KNOW?    Tilted TownDD-035

    DD-035Science+ Locations

    Tilted Town

    This Mexican village is built on a tilt to fool your balance.

    Open case file →
  5. 05
    DID YOU
    KNOW?    Static SprayDD-051

    DD-051Tech+ Science

    Static Spray

    Static electricity holds this paint in place.

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  6. 06
    DID YOU
    KNOW?    Torque ConversionDD-075

    DD-075Cars+ Tech

    Torque Conversion

    How an automatic moves without a clutch pedal.

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  7. 07
    DID YOU
    KNOW?    Liquid LightsDD-073

    DD-073Science+ Tech

    Liquid Lights

    Why salt water conducts and pure water barely does.

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  8. 08
    DID YOU
    KNOW?    Branched FlowDD-739

    DD-739Science

    Branched Flow

    A laser inside a soap film splits into branching filaments.

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  9. 09
    DID YOU
    KNOW?    Golf BallingDD-695

    DD-695Science+ Tech

    Golf Balling

    Squash, then spring.

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  10. 10
    DID YOU
    KNOW?    Counter CraneDD-687

    DD-687Tech+ Science

    Counter Crane

    Balance is the real lift.

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  11. 11
    DID YOU
    KNOW?    UV FaceDD-654

    DD-654Science+ Tech

    UV Face

    Under UV, sunscreen goes dark.

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  12. 12
    DID YOU
    KNOW?    Cloud ChambersDD-623

    DD-623Science+ History

    Cloud Chambers

    Radiation, made visible.

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  13. 13
    DID YOU
    KNOW?    Around the RainbowDD-651

    DD-651Science+ Nature

    Around the Rainbow

    Rainbows are secretly circles.

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  14. 14
    DID YOU
    KNOW?    Point CurieDD-669

    DD-669Science+ Tech

    Point Curie

    Too hot to stick.

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  15. 15
    DID YOU
    KNOW?    Central LimitsDD-588

    DD-588Science

    Central Limits

    Random bounces, one bell curve.

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  16. 16
    DID YOU
    KNOW?    Microwave MetalDD-589

    DD-589Science

    Microwave Metal

    Lightning in a microwave.

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  17. 17
    DID YOU
    KNOW?    Newtons CradleDD-286

    DD-286Science

    Newtons Cradle

    Lift one ball, and one ball answers.

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  18. 18
    DID YOU
    KNOW?    Making Plasma in the MicrowaveDD-287

    DD-287Science

    Making Plasma in the Microwave

    A glowing ball of plasma can appear inside a kitchen microwave.

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  19. 19
    DID YOU
    KNOW?    Getting to the (Ball)PointDD-304

    DD-304Tech

    Getting to the (Ball)Point

    A ballpoint writes with a tiny rolling ball.

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  20. 20
    DID YOU
    KNOW?    Is Water Sticky?DD-296

    DD-296Science

    Is Water Sticky?

    A coin can hold a dome of water above its edge.

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  21. 21
    DID YOU
    KNOW?    A Real Hot HeadDD-300

    DD-300Science

    A Real Hot Head

    A safety match needs the box to light.

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  22. 22
    DID YOU
    KNOW?    Video TrickeryDD-301

    DD-301Tech+ Science

    Video Trickery

    Phone videos can bend propellers.

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  23. 23
    DID YOU
    KNOW?    Linking UpDD-302

    DD-302Science+ Nature

    Linking Up

    Storm clouds sort charge until the air gives way.

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  24. 24
    DID YOU
    KNOW?    PlasmaDD-113

    DD-113Science

    Plasma

    Most visible matter in the universe is plasma.

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  25. 25
    DID YOU
    KNOW?    Quartz CrystalsDD-168

    DD-168Science+ Tech

    Quartz Crystals

    Squeeze a quartz crystal and it makes electricity.

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  26. 26
    DID YOU
    KNOW?    Fire WorksDD-155

    DD-155Science

    Fire Works

    Strontium burns red, copper blue-green.

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  27. 27
    DID YOU
    KNOW?    CASCADEDD-269

    DD-269Science+ Nature

    CASCADE

    A water drop can bounce and shrink several times before it vanishes.

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  28. 28
    DID YOU
    KNOW?    You're Spinning Me AroundDD-274

    DD-274Science+ Tech

    You're Spinning Me Around

    A spinning gyroscope resists any change to its axis.

    Open case file →
  29. 29
    DID YOU
    KNOW?    The Strings of FateDD-319

    DD-319Science+ Space

    The Strings of Fate

    Some versions of string theory need 10 or 11 dimensions.

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  30. 30
    DID YOU
    KNOW?    See Right Through MeDD-332

    DD-332Science

    See Right Through Me

    Pyrex dipped in vegetable oil seems to disappear.

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  31. 31
    DID YOU
    KNOW?    SudsyDD-345

    DD-345Science

    Sudsy

    Soap molecules have one end that loves water and one that loves oil.

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  32. 32
    DID YOU
    KNOW?    Computer Wave ControlDD-356

    DD-356Tech+ Science

    Computer Wave Control

    Computer-timed wave makers can hold a wave in place.

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  33. 33
    DID YOU
    KNOW?    Acoustic LevitationDD-394

    DD-394Science

    Acoustic Levitation

    Sound waves can hold water droplets in midair.

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  34. 34
    DID YOU
    KNOW?    Video Trickery IIDD-461

    DD-461Tech+ Science

    Video Trickery II

    On video, a helicopter's rotor can seem to stand still.

    Open case file →

Collection Quiz

All quizzes →

68 questions from all 34 case files in Everyday Physics. Test Your Knowledge: answers are revealed instantly.

  1. In the Marangoni effect, which way does liquid flow?

    1. From high to low surface tension
    2. From low to high surface tension
    3. Only downhill
    4. Only toward heat
    Show the answer

    Answer: B. From low to high surface tension Now You Know: Higher-tension regions pull harder, so fluid flows from low toward high surface tension. Source: DD-024 · Marangoni Motion · Write-up · Exhibit A (Flow along a surface-tension gradient) · Marangoni effect (Wikipedia); Numerical Analysis of Effect of Surface Active Elements on Marangoni Convection (COMSOL conference paper); Surface Defects: Causes, Prevention, and Remedies (coatings handbook chapter, Wiley)

  2. Which everyday sight is a classic example of the Marangoni effect?

    1. Rainbows
    2. 'Tears' running down a wine glass
    3. Ice floating
    4. Boiling water
    Show the answer

    Answer: B. 'Tears' running down a wine glass Now You Know: Alcohol evaporating from the film raises its surface tension and pulls wine up the glass. Source: DD-024 · Marangoni Motion · Write-up · Exhibit C (Tears of wine) · Tears of wine: new insights on an old phenomenon (Scientific Reports, 2015); Marangoni effect (Wikipedia)

  3. 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)

  4. 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)

  5. In water, light travels at roughly what fraction of its speed in a vacuum?

    1. About 25%
    2. About 75%
    3. About 99.9%
    4. About 150%
    Show the answer

    Answer: B. About 75% Now You Know: Light slows to about 75% of its vacuum speed in water, so fast particles can outrun it there. Source: DD-020 · Cherenkov Glow · Write-up · Exhibit B (Water slows light to 75%) · Cherenkov Radiation, Explained (U.S. Department of Energy, Office of Nuclear Energy, 2023); What is Cherenkov Radiation? (IAEA); What is Cerenkov Radiation? (Hong Kong Observatory)

  6. Cherenkov radiation is often compared to which everyday effect?

    1. A rainbow
    2. An echo
    3. A sonic boom
    4. Static electricity
    Show the answer

    Answer: C. A sonic boom Now You Know: It's a 'shockwave' of light, the optical version of a sonic boom. Source: DD-020 · Cherenkov Glow · Write-up · Exhibit D (A sonic boom for light) · Cherenkov Radiation, Explained (U.S. Department of Energy, Office of Nuclear Energy, 2023); What is Cherenkov Radiation? (IAEA); Cherenkov radiation (Wikipedia)

  7. Which park is home to Mexico's 'tilted town'?

    1. Xcaret
    2. Xplor
    3. Xenses
    4. Xel-Há
    Show the answer

    Answer: C. Xenses Now You Know: El Pueblo is part of Xenses, Grupo Xcaret's sensory park. Source: DD-035 · Tilted Town · Write-up · Exhibit B (El Pueblo) · Entrada Xenses: Parque Sensorial (Grupo Xcaret official site); Preguntas Frecuentes Xenses (Grupo Xcaret official FAQ)

  8. What city is Xenses actually right next to?

    1. Mexico City
    2. Playa del Carmen
    3. Tulum
    4. Mérida
    Show the answer

    Answer: B. Playa del Carmen Now You Know: It's just past Playa del Carmen, about 74 km from Cancún. Source: DD-035 · Tilted Town · Write-up · Exhibit A (Where it is) · Entrada Xenses: Parque Sensorial (Grupo Xcaret official site); Preguntas Frecuentes Xenses (Grupo Xcaret official FAQ); El Pueblito al Revés de Xenses: El lugar que desafía tu mente (Alternativo, July 2025)

  9. What holds powder on the part before curing?

    1. Glue
    2. Electrostatic charge
    3. Magnets
    4. Water
    Show the answer

    Answer: B. Electrostatic charge Now You Know: Charged powder is attracted to the grounded part and stays put. Source: DD-051 · Static Spray · Write-up · Exhibit B (Charge and ground) · What is Powder Coating? (Powder Coating Institute); Powder Coating Painting System (Pollution Prevention InfoHouse); Powder Coat Applications Final Report (U.S. EPA)

  10. What turns the loose powder into a hard coating?

    1. Air drying
    2. A curing oven
    3. UV light
    4. Freezing
    Show the answer

    Answer: B. A curing oven Now You Know: It's baked at about 325–450 °F, where it melts and cross-links. Source: DD-051 · Static Spray · Write-up · Exhibit C (The oven does the rest) · What is Powder Coating? (Powder Coating Institute); Sustainability: VOC Elimination (Powder Coating Institute); Powder Coat Applications Final Report (U.S. EPA)

  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 carries current through salt water?

    1. Free electrons
    2. Dissolved ions
    3. Photons
    4. Water molecules
    Show the answer

    Answer: B. Dissolved ions Now You Know: Salts split into positive and negative ions. Source: DD-073 · Liquid Lights · Write-up · Exhibit A (Ions carry the current) · Conductometry monograph (Metrohm)

  14. Theoretical conductivity of pure water at 25 °C?

    1. Exactly zero
    2. 0.055 µS/cm
    3. 1 mS/cm
    4. 0.053 S/cm
    Show the answer

    Answer: B. 0.055 µS/cm Now You Know: It comes from water splitting slightly into ions. Source: DD-073 · Liquid Lights · Write-up · Exhibit B (Pure water isn't ion-free) · Conductometry monograph (Metrohm); Traceable standards for electrolytic conductivity measurements (CHIMIA, 2009)

  15. In which kind of wave was branched flow first observed?

    1. Light
    2. Electrons
    3. Sound
    4. Gravity waves
    Show the answer

    Answer: B. Electrons Now You Know: It was first seen for electrons, then microwaves. Source: DD-739 · Branched Flow · Write-up · Exhibit A (The phenomenon) · Patsyk et al. (2020), Observation of branched flow of light, Nature

  16. When was branched flow of light first reported?

    1. 1905
    2. 1970
    3. 2020
    4. 2025
    Show the answer

    Answer: C. 2020 Now You Know: In Nature in 2020. Source: DD-739 · Branched Flow · Write-up · Exhibit B (First in light) · Patsyk et al. (2020), Observation of branched flow of light, Nature; Nature Video (2020): A laser show in a soap bubble

  17. What does COR compare?

    1. Rebound speed to impact speed
    2. Weight to size
    3. Spin to height
    4. Dimples to cover area
    Show the answer

    Answer: A. Rebound speed to impact speed Now You Know: Speed after the collision divided by speed before it. Source: DD-695 · Golf Balling · Write-up · Exhibit A (What COR measures) · Wikipedia: Coefficient of restitution

  18. What initial-velocity limit do the rules set (before tolerance)?

    1. 150 ft/s
    2. 250 ft/s
    3. 350 ft/s
    4. 500 ft/s
    Show the answer

    Answer: B. 250 ft/s Now You Know: 250 ft/s, plus a 2% tolerance. Source: DD-695 · Golf Balling · Write-up · Exhibit C (How the rules test it) · USGA/R&A: Initial Velocity Test Protocol

  19. When does a crane tip over?

    1. When overturning moment exceeds stabilizing moment
    2. When the load is over 10 t
    3. When the boom is vertical
    4. When the engine stalls
    Show the answer

    Answer: A. When overturning moment exceeds stabilizing moment Now You Know: It's a balance of moments. Source: DD-687 · Counter Crane · Write-up · Exhibit A (Moments, not just weight) · WorkSafe Queensland: Mobile crane code of practice 2024

  20. What do the '10 t' slabs in the footage show?

    1. Counterweight mass
    2. Boom length
    3. Fuel capacity
    4. Hook speed
    Show the answer

    Answer: A. Counterweight mass Now You Know: Each counterweight slab's mass. Source: DD-687 · Counter Crane · Write-up · Exhibit B (Counterweights) · WorkSafe Queensland: Mobile crane code of practice 2024; SANY Group: How to read a crane load chart

  21. Why does sunscreen look dark on a UV camera?

    1. It stops UV light coming back from the skin
    2. It's dyed black
    3. It absorbs visible light
    4. The camera is faulty
    Show the answer

    Answer: A. It stops UV light coming back from the skin Now You Know: Sunscreen stops most UV, so little comes back to the camera. Source: DD-654 · UV Face · Write-up · Exhibit A (What the camera sees) · Cole et al. (2016), Metal oxide sunscreens protect skin by absorption, not by reflection or scattering, Photodermatology, Photoimmunology & Photomedicine; Pratt et al. (2017), UV imaging reveals facial areas that are prone to skin cancer are disproportionately missed during sunscreen application, PLOS ONE

  22. About how much UV do zinc oxide and titanium dioxide reflect?

    1. About 4-5%
    2. About 50%
    3. About 95%
    4. None
    Show the answer

    Answer: A. About 4-5% Now You Know: About 4-5%. Source: DD-654 · UV Face · Write-up · Exhibit B (Absorb, not reflect) · Cole et al. (2016), Metal oxide sunscreens protect skin by absorption, not by reflection or scattering, Photodermatology, Photoimmunology & Photomedicine; National Academies (2022): Review of fate, exposure and effects of sunscreens, ch. 2, Introduction to sunscreens and their UV filters

  23. What makes a cloud-chamber track?

    1. Droplets condensing on ions
    2. Light given off by the particle
    3. Sparks between wires
    4. Bubbles in boiling liquid
    Show the answer

    Answer: A. Droplets condensing on ions Now You Know: Vapor condenses on the ions a charged particle leaves behind. Source: DD-623 · Cloud Chambers · Write-up · Exhibit A (Why droplets form) · NobelPrize.org: C.T.R. Wilson, Nobel Prize in Physics 1927 (facts); C.T.R. Wilson: Nobel Lecture (1927), On the cloud method of making visible ions and the tracks of ionizing particles

  24. Why are the tracks visible?

    1. A lamp lights the droplets
    2. The droplets glow
    3. The vapor is radioactive
    4. The walls fluoresce
    Show the answer

    Answer: A. A lamp lights the droplets Now You Know: The droplets scatter light; they don't glow. Source: DD-623 · Cloud Chambers · Write-up · Exhibit B (Not glowing) · C.T.R. Wilson: Nobel Lecture (1927), On the cloud method of making visible ions and the tracks of ionizing particles

  25. About how far from the antisolar point does the primary rainbow form?

    1. About 42°
    2. About 4°
    3. About 90°
    4. About 180°
    Show the answer

    Answer: A. About 42° Now You Know: About 40 to 42°. Source: DD-651 · Around the Rainbow · Write-up · Exhibit A (Refract, reflect, refract) · HyperPhysics (Georgia State University): Primary and secondary rainbows; National Geographic Education: Rainbow

  26. Where is the antisolar point?

    1. Directly opposite the sun
    2. At the sun
    3. Straight overhead
    4. Due north
    Show the answer

    Answer: A. Directly opposite the sun Now You Know: Where the shadow of your head falls. Source: DD-651 · Around the Rainbow · Write-up · Exhibit A (Refract, reflect, refract) · HyperPhysics (Georgia State University): Primary and secondary rainbows; National Geographic Education: Rainbow

  27. Who is the Curie point named after?

    1. Pierre Curie
    2. Marie Curie
    3. Ève Curie
    4. Irène Joliot-Curie
    Show the answer

    Answer: A. Pierre Curie Now You Know: His 1895 thesis. Source: DD-669 · Point Curie · Write-up · Exhibit A (Named for Pierre Curie) · Britannica: Curie point; Pierre Curie (1895): Propriétés magnétiques des corps à diverses températures (Internet Archive)

  28. About what is iron's Curie temperature?

    1. About 770 °C
    2. About 77 °C
    3. About 7,700 °C
    4. About 0 °C
    Show the answer

    Answer: A. About 770 °C Now You Know: Nickel's is about 358 °C. Source: DD-669 · Point Curie · Write-up · Exhibit D (The numbers) · Britannica: Curie point; Supermagnete: Curie temperature, explanations and illustrations

  29. What does a bead do at each peg of a Galton board?

    1. Bounces left or right
    2. Stops
    3. Splits in two
    4. Rolls back up
    Show the answer

    Answer: A. Bounces left or right Now You Know: The counts follow a binomial distribution. Source: DD-588 · Central Limits · Write-up · Exhibit A (Left or right) · Wikipedia: Galton board; Four Pines Publishing: The Galton Board

  30. What shape do the beads form with many rows and beads?

    1. A bell curve
    2. A straight line
    3. A spiral
    4. A U shape
    Show the answer

    Answer: A. A bell curve Now You Know: The normal distribution. Source: DD-588 · Central Limits · Write-up · Exhibit B (Toward the bell) · Wikipedia: Galton board; Kunert, Montag & Pöhlmann, The quincunx: history and mathematics, Statistical Papers (2001)

  31. What does metal do to microwaves?

    1. Reflects them
    2. Absorbs all of them
    3. Slows them to a stop
    4. Turns them into light
    Show the answer

    Answer: A. Reflects them Now You Know: Food absorbs them; metal reflects them. Source: DD-589 · Microwave Metal · Write-up · Exhibit A (Metal reflects) · MIT School of Engineering: Why can't we put metal objects in a microwave?; Scientific American: Why do metal objects create sparks when placed inside a microwave oven? (1999)

  32. Where is the electric field on metal strongest?

    1. At sharp points and edges
    2. At the center of flat sheets
    3. Inside hollow tubes
    4. Nowhere in particular
    Show the answer

    Answer: A. At sharp points and edges Now You Know: That's where arcs start. Source: DD-589 · Microwave Metal · Write-up · Exhibit B (Points and edges) · MIT School of Engineering: Why can't we put metal objects in a microwave?; Scientific American: Why do metal objects create sparks when placed inside a microwave oven? (1999)

  33. How are the balls arranged?

    1. Touching in a row
    2. Stacked vertically
    3. Spread far apart
    4. In a circle
    Show the answer

    Answer: A. Touching in a row Now You Know: They hang so each just touches the next. Source: DD-286 · Newtons Cradle · Write-up · Exhibit A (Identical balls) · Wikipedia: Newton's cradle

  34. What happens when one end ball is released?

    1. One ball swings out the far end
    2. All balls swing
    3. Nothing moves
    4. The middle ball jumps
    Show the answer

    Answer: A. One ball swings out the far end Now You Know: Two in gives two out. Source: DD-286 · Newtons Cradle · Write-up · Exhibit B (One in, one out) · Wikipedia: Newton's cradle

  35. What is plasma?

    1. Ionized gas
    2. Superheated water
    3. A type of metal
    4. Liquid light
    Show the answer

    Answer: A. Ionized gas Now You Know: Free electrons make it conduct and glow. Source: DD-287 · Making Plasma in the Microwave · Write-up · Exhibit A (Ionized gas) · Wikipedia: Plasma (physics)

  36. Where does microwave plasma usually start?

    1. At sharp metal edges or between grape halves
    2. In the oven's fan
    3. In the door glass
    4. Anywhere at random
    Show the answer

    Answer: A. At sharp metal edges or between grape halves Now You Know: Those spots concentrate the field. Source: DD-287 · Making Plasma in the Microwave · Write-up · Exhibit B (Concentrated fields) · Khattak et al., PNAS (2019): Linking plasma formation in grapes to microwave resonances of aqueous dimers

  37. What are ballpoint balls usually made of?

    1. Steel, brass or tungsten carbide
    2. Glass
    3. Plastic
    4. Gold
    Show the answer

    Answer: A. Steel, brass or tungsten carbide Now You Know: They have to resist wear. Source: DD-304 · Getting to the (Ball)Point · Write-up · Exhibit A (Hard ball tip) · Wikipedia: Ballpoint pen

  38. How does the ink reach the paper?

    1. The rolling ball carries it
    2. Gravity drips it
    3. A pump sprays it
    4. A felt wick spreads it
    Show the answer

    Answer: A. The rolling ball carries it Now You Know: The ball also seals the reservoir. Source: DD-304 · Getting to the (Ball)Point · Write-up · Exhibit B (Rolling ink) · Wikipedia: Ballpoint pen

  39. What attracts water molecules to each other?

    1. Hydrogen bonds
    2. Magnetism
    3. Gravity
    4. Static from air
    Show the answer

    Answer: A. Hydrogen bonds Now You Know: That's the root of surface tension. Source: DD-296 · Is Water Sticky? · Write-up · Exhibit A (Hydrogen bonds) · Wikipedia: Surface tension

  40. Why does the surface act like a film?

    1. Surface molecules are pulled inward
    2. Air pushes down
    3. Dust forms a layer
    4. Light hardens it
    Show the answer

    Answer: A. Surface molecules are pulled inward Now You Know: They lack neighbors above. Source: DD-296 · Is Water Sticky? · Write-up · Exhibit B (A stretched film) · Wikipedia: Surface tension

  41. What oxidizer is in a match head?

    1. Potassium chlorate
    2. Table salt
    3. Baking soda
    4. Sugar
    Show the answer

    Answer: A. Potassium chlorate Now You Know: It releases oxygen. Source: DD-300 · A Real Hot Head · Write-up · Exhibit A (The head) · Wikipedia: Match

  42. What's on a safety match's striker?

    1. Red phosphorus and glass
    2. Sulfur only
    3. Sandpaper only
    4. Magnesium
    Show the answer

    Answer: A. Red phosphorus and glass Now You Know: That's why safety matches need the box. Source: DD-300 · A Real Hot Head · Write-up · Exhibit B (The striker) · Wikipedia: Match

  43. How does a rolling shutter read a frame?

    1. Row by row
    2. All at once
    3. Randomly
    4. By color
    Show the answer

    Answer: A. Row by row Now You Know: Usually top to bottom. Source: DD-301 · Video Trickery · Write-up · Exhibit A (Row by row) · Wikipedia: Rolling shutter

  44. Which sensors commonly use rolling shutters?

    1. CMOS
    2. Film
    3. Vacuum tubes
    4. Mirrors
    Show the answer

    Answer: A. CMOS Now You Know: Many phone cameras do. Source: DD-301 · Video Trickery · Write-up · Exhibit B (CMOS sensors) · Wikipedia: Rolling shutter

  45. What separates charge in storm clouds?

    1. Collisions of ice, graupel and droplets
    2. Sunlight
    3. Wind on the ground
    4. Magnetism
    Show the answer

    Answer: A. Collisions of ice, graupel and droplets Now You Know: Strong updrafts drive it. Source: DD-302 · Linking Up · Write-up · Exhibit A (Charge separation) · NOAA NSSL: Severe Weather 101: Lightning; Wikipedia: Lightning

  46. Which part of the cloud is usually positive?

    1. The top
    2. The bottom
    3. The middle only
    4. None
    Show the answer

    Answer: A. The top Now You Know: The lower region is negative. Source: DD-302 · Linking Up · Write-up · Exhibit B (Positive on top) · NOAA NSSL: Severe Weather 101: Lightning; National Weather Service: Lightning Science overview

  47. What is plasma often called?

    1. The fourth state of matter
    2. A liquid
    3. A solid
    4. A vacuum
    Show the answer

    Answer: A. The fourth state of matter Now You Know: After solid, liquid and gas. Source: DD-113 · Plasma · Write-up · Exhibit A (Fourth state) · Wikipedia: Plasma (physics)

  48. What happens to atoms in plasma?

    1. Electrons are stripped
    2. They freeze
    3. They vanish
    4. They merge
    Show the answer

    Answer: A. Electrons are stripped Now You Know: Leaving ions. Source: DD-113 · Plasma · Write-up · Exhibit B (Ionized) · Wikipedia: Plasma (physics)

  49. What is quartz made of?

    1. Silicon and oxygen
    2. Carbon
    3. Iron and sulfur
    4. Aluminum
    Show the answer

    Answer: A. Silicon and oxygen Now You Know: SiO2. Source: DD-168 · Quartz Crystals · Write-up · Exhibit A (Silicon dioxide) · Wikipedia: Quartz

  50. How common is quartz?

    1. Very common in the crust
    2. Extremely rare
    3. Only in meteorites
    4. Only underwater
    Show the answer

    Answer: A. Very common in the crust Now You Know: Among the most common minerals. Source: DD-168 · Quartz Crystals · Write-up · Exhibit B (Common mineral) · Wikipedia: Quartz

  51. What produces firework colors?

    1. Metal salts
    2. Food dye
    3. Paint
    4. Glass
    Show the answer

    Answer: A. Metal salts Now You Know: Heated in the burst. Source: DD-155 · Fire Works · Write-up · Exhibit A (Flame test) · Wikipedia: Flame test

  52. Which metal gives red?

    1. Strontium
    2. Copper
    3. Sodium
    4. Barium
    Show the answer

    Answer: A. Strontium Now You Know: Lithium too. Source: DD-155 · Fire Works · Write-up · Exhibit B (Strontium red) · Wikipedia: Flame test; Wikipedia: Fireworks

  53. What is the process called?

    1. A coalescence cascade
    2. Evaporation
    3. Condensation
    4. Sublimation
    Show the answer

    Answer: A. A coalescence cascade Now You Know: Stage after stage. Source: DD-269 · CASCADE · Write-up · Exhibit A (Bounce) · Wikipedia: Coalescence (physics)

  54. Why does the drop bounce?

    1. A thin air film
    2. Magnetism
    3. Heat
    4. Wind
    Show the answer

    Answer: A. A thin air film Now You Know: Air must drain away. Source: DD-269 · CASCADE · Write-up · Exhibit B (Partial merge) · Wikipedia: Coalescence (physics)

  55. What principle keeps a gyroscope steady?

    1. Conservation of angular momentum
    2. Magnetism
    3. Buoyancy
    4. Friction
    Show the answer

    Answer: A. Conservation of angular momentum Now You Know: A spinning rotor. Source: DD-274 · You're Spinning Me Around · Write-up · Exhibit A (Rotor) · Wikipedia: Gyroscope

  56. What does it resist?

    1. Changes to its axis
    2. Gravity entirely
    3. Heat
    4. Light
    Show the answer

    Answer: A. Changes to its axis Now You Know: While spinning. Source: DD-274 · You're Spinning Me Around · Write-up · Exhibit B (Angular momentum) · Wikipedia: Gyroscope; Wikipedia: Angular momentum

  57. What are particles in string theory?

    1. Vibrating strings
    2. Tiny balls
    3. Waves of sound
    4. Magnets
    Show the answer

    Answer: A. Vibrating strings Now You Know: One-dimensional. Source: DD-319 · The Strings of Fate · Write-up · Exhibit A (Strings) · Wikipedia: String theory

  58. How many dimensions does M-theory use?

    1. 11
    2. 4
    3. 26
    4. 3
    Show the answer

    Answer: A. 11 Now You Know: Superstrings use 10. Source: DD-319 · The Strings of Fate · Write-up · Exhibit B (10 dimensions) · Wikipedia: String theory

  59. Why does Pyrex vanish in oil?

    1. Similar refractive index
    2. It dissolves
    3. It melts
    4. It is painted
    Show the answer

    Answer: A. Similar refractive index Now You Know: Light bends alike. Source: DD-332 · See Right Through Me · Write-up · Exhibit A (Index) · Wikipedia: Borosilicate glass

  60. About what is Pyrex's index?

    1. 1.47
    2. 1.00
    3. 2.42
    4. 3.50
    Show the answer

    Answer: A. 1.47 Now You Know: Borosilicate. Source: DD-332 · See Right Through Me · Write-up · Exhibit B (Oil) · Wikipedia: Refractive index

  61. How is soap made?

    1. Saponification
    2. Distillation
    3. Fermentation
    4. Smelting
    Show the answer

    Answer: A. Saponification Now You Know: Fat plus base. Source: DD-345 · Sudsy · Write-up · Exhibit A (Made by) · Wikipedia: Soap

  62. What traps grease?

    1. Micelles
    2. Bubbles only
    3. Salt
    4. Heat
    Show the answer

    Answer: A. Micelles Now You Know: Clusters. Source: DD-345 · Sudsy · Write-up · Exhibit B (Head) · Wikipedia: Soap

  63. What forms a standing wave?

    1. Two opposing waves
    2. One wave
    3. Wind
    4. Rain
    Show the answer

    Answer: A. Two opposing waves Now You Know: Interference. Source: DD-356 · Computer Wave Control · Write-up · Exhibit A (Two waves) · Wikipedia: Standing wave

  64. What are still points called?

    1. Nodes
    2. Peaks
    3. Troughs
    4. Crests
    Show the answer

    Answer: A. Nodes Now You Know: No motion. Source: DD-356 · Computer Wave Control · Write-up · Exhibit B (Nodes) · Wikipedia: Standing wave

  65. What lifts the droplets?

    1. Sound
    2. Magnets
    3. Air jets
    4. Strings
    Show the answer

    Answer: A. Sound Now You Know: Ultrasound. Source: DD-394 · Acoustic Levitation · Write-up · Exhibit A (Sound) · Wikipedia: Acoustic levitation

  66. Where do droplets sit?

    1. At pressure nodes
    2. On the transducer
    3. On the floor
    4. Randomly
    Show the answer

    Answer: A. At pressure nodes Now You Know: Quiet points. Source: DD-394 · Acoustic Levitation · Write-up · Exhibit B (Standing wave) · Wikipedia: Acoustic levitation

  67. What is frame rate measured in?

    1. Frames per second
    2. Meters
    3. Volts
    4. Hertz only
    Show the answer

    Answer: A. Frames per second Now You Know: FPS. Source: DD-461 · Video Trickery II · Write-up · Exhibit A (Frames) · Wikipedia: Wagon-wheel effect

  68. Why do blades look still?

    1. Rotation matches frame rate
    2. They stop
    3. Camera is broken
    4. Wind
    Show the answer

    Answer: A. Rotation matches frame rate Now You Know: Sync. Source: DD-461 · Video Trickery II · Write-up · Exhibit B (Sync) · Wikipedia: Wagon-wheel effect