Book 13 activities
Try it at home: 150 science activities from Book 13
Every question in A Million Whys Book 13, The Light Expedition, ends with a "Think like a scientist" idea. Here they are in one place. Each one links to its question page, with the video and the full answer.
Expedition 1: Sunbeams & Shadows (25)
1. Why Does Light Travel in Straight Lines?
Use a pencil tip to poke a hole in the middle of three index cards. Stand them up in a row, line up the holes, and shine a flashlight through. Slide one card sideways and the beam stops.
2. Why Is Light the Fastest Thing There Is?
Flip a light switch and try to spot any delay between your finger moving and the room lighting up. You will not find one, because light is just too fast for your eyes to catch.
3. Why Does Sunshine Take About Eight Minutes to Reach Earth?
Set a timer for 8 minutes and tidy your room. When it rings, the sunlight coming through your window left the Sun just as you started. What else could you do in 8 minutes?
4. Why Can You See a Sunbeam Streaming Through Dusty Air?
Close the curtains in a room so only a thin stripe of sunlight comes in. Gently shake a clean towel near the beam and watch the dust sparkle in it. Never look straight at the Sun.
5. Why Are the Spots of Sunlight Under a Tree Round?
Next time you are under a leafy tree on a sunny day, hold your hands in front of you with your fingers crossed in a waffle pattern. Watch the round spots appear on the ground. Never look up at the Sun.
6. Why Can a Shadow Look Sharp One Minute and Fuzzy the Next?
Hold a pencil near a white wall with a lamp or flashlight pointing at it. Slowly move the pencil toward and away from the wall, and watch the edge of the shadow get sharper and fuzzier.
Do this with a grown-up7. Why Do You Get More than One Shadow Under Several Lamps?
With a grown-up, switch on two lamps in a darkened room (or use two flashlights). Stand your hand in front of a wall and count how many shadows you can make. Which parts are darkest?
Do this with a grown-up8. Why Are Shadows on Snow Sometimes Blue?
On a sunny winter day, step outside and look closely at the shadow of a tree or a fence on the snow. Look for the blue tint. Next time, try to spot blue shadows on other bright surfaces too.
Do this with a grown-up9. Why Can a Flashlight and Your Hands Make a Shadow Animal?
In a dim room, aim a flashlight at a blank wall. Make a bird, a dog, or a rabbit with your hands. Slide your hands closer to the light to make your animal grow into a giant.
10. Why Does a Glass of Water Throw a Bright, Wiggly Shadow?
Put a clear glass of water on a sheet of white paper in bright sunshine near a window. Look at the shadow it makes, and find the bright curved line inside it. Gently tap the table to see it wiggle.
11. Why Is It Cooler in the Shade than in the Sun?
Put one thermometer in direct sun and another in the shade on a warm day. Wait a few minutes, then compare their readings. Which one is hotter, and by how many degrees?
12. Why Do Dark Clothes Feel Hotter in the Sun than Light Ones?
Lay a black sheet of paper and a white sheet of paper side by side in the sun. After ten minutes, hold the back of your hand a few centimeters above each. Which one feels warmer?
13. Why Does Sunshine Feel Warm on Your Face Even When the Air Is Cold?
On a cool day, stand in a sunny spot and then step into the shade. Notice how the warm feeling on your face disappears. Where did it go?
14. Why Can a Cardboard Solar Oven Cook with Only Sunshine?
With a grown-up, make a pizza-box solar oven with foil, black paper, and plastic wrap. Warm a s’more or a cheese slice. Wear sunglasses, never look at the bright foil, and use oven mitts.
Do this with a grown-up15. Why Does Snow Melt First Around a Dark Rock?
On a sunny day with snow on the ground, put a dark stone on the snow and a white stone beside it. Check them after an hour. Which one has sunk deeper?
16. Why Do Houseplants Lean Toward a Window?
Place a houseplant beside a window and turn it so the leaves face away from the glass. Look again after a few days. Which way are the stems bending now?
17. Why Does the Bright Patch From a Window Slide Across the Floor?
Stick a piece of tape on the floor at the edge of a sunny patch, and mark the time. Check an hour later and mark the new spot. How far did the light patch travel?
18. Why Is a Cloudy Day Outside Still Brighter than a Lit Room Inside?
Look at a bright window from inside the house, then step outside on a cloudy day. Notice how the room looks dim after you have been in the daylight. Why did your eyes get fooled?
Do this with a grown-up19. Why Do Shadows Disappear on Cloudy Days?
On a cloudy day, hold a pencil above a white sheet of paper outdoors and look for a shadow. Try again on a sunny day. What changed?
Do this with a grown-up20. Why Does Your Shadow Stretch, Shrink, and Stretch Again as You Walk Past a Streetlamp?
At dusk, with a grown-up, walk past a streetlamp and watch your shadow. Ask a friend to mark where your shadow ends at three spots. When was it shortest?
Do this with a grown-up21. Why Does Your Hand Make a Giant Shadow When It Is Close to a Lamp?
Shine a flashlight on a wall and hold a toy in front of it. Move the toy toward the flashlight, then away. How big can you make its shadow?
22. Why Can You See the Shadow of a Cloud Sliding Across a Field?
On a partly cloudy, breezy day, find a spot with a big view, like a hill or a playground. Watch the patches of shadow and sunshine move. How fast can you follow one with your eyes?
23. Why Does Your Shadow Always Follow You?
Play shadow tag outdoors on a sunny day. Try to stomp on a friend’s shadow without touching them. Can you escape your own shadow by running?
Do this with a grown-up24. Why Do Beams of Sunlight Fan Out From Behind a Cloud?
On a day with scattered clouds, look at a gap in the clouds when the Sun is low. Draw the beams you see. Do not look straight at the Sun, and look only at the beams.
25. Why Do Tall Buildings Leave Long, Cool Shadows on City Streets?
On a sunny day, find the shadow of a tall building or a tall tree. Place a stone at the tip of the shadow, and check again an hour later. Did it grow, shrink, or move?
Expedition 2: Mixing Colors & Filters (25)
26. Why Do Red, Green, and Blue Lights Mix to Make White Light?
In a dim room, cover three flashlights with red, green, and blue cellophane (hold it on with rubber bands). Shine them on a white wall so the circles overlap, and see what colors appear in the middle.
27. Why Do Paints Mix Differently From Colored Lights?
Mix a blob of red paint with a blob of green paint on paper and note the color. Then think about what happens with red and green flashlights. How is it different?
28. Why Can You Make Almost Any Color From Just Three Paints?
Squeeze out just red, yellow, and blue (plus white) and see how many different colors you can mix. Label each one with the recipe you used, like “two parts blue + one part yellow.”
29. Why Does Mixing All Your Paints Make a Muddy Brown?
Mix one drop each of every color on a plate, a little at a time. Watch how the mixture changes. At what point did your colors turn muddy?
30. Why Does a Red Cellophane Sheet Change What You See?
Look through red cellophane at a drawing made with red, green, and blue markers. Which colors seem to disappear, and which turn dark?
31. Why Do Colors Look Different Under Different Lamps?
With a grown-up, look at a colorful toy under a warm yellow lamp and then under a cool white one. Which colors changed most? Try looking at it in daylight too.
Do this with a grown-up32. Why Do Some People See Some Colors Differently?
Make a poster that uses patterns and labels, not just color, to show different things (like stripes for one group and dots for another). Could everyone read it easily?
33. Why Do Screens Use Only Red, Green, and Blue Dots?
With a grown-up’s permission, hold a magnifying glass up to a TV or tablet showing a white or yellow picture. Look for the tiny dots. What colors do you see?
Do this with a grown-up34. How Does the Color of Paper Change How Much Light Bounces Back?
In a dim room, shine a flashlight on a sheet of white paper and then on black paper. Which one lights up the room more? Which one feels warmer after a few minutes in the sun?
35. Why Do Two Colored Flashlights Make Colored Shadows?
Stand a toy in front of a white wall. Shine a red flashlight (or a flashlight with red cellophane) from one side and a green one from the other. What colors are the two shadows?
36. Why Does a Spinning Color Wheel Turn White?
With a grown-up, cut a circle from cardboard and color it in seven slices of rainbow colors. Push a pencil through the center and spin it. What color do you see?
Do this with a grown-up37. Why Does the Same Gray Look Lighter or Darker on Different Backgrounds?
Cut two identical gray squares from paper. Place one on white paper and one on black paper. Do they look the same? Then slide them side by side to check.
Do this with a grown-up38. Why Do Secret Decoder Windows Reveal Hidden Messages?
Write a secret word in green or blue marker on white paper. Cover it with lots of red scribbles. Look through red cellophane to read it.
39. Why Does Adding White Paint Make a Color Lighter?
Put a small blob of blue paint on a plate. Add a tiny bit of white, mix, and paint a stripe. Keep adding white a little at a time. How many different blues can you make?
40. Why Does Wet Sand Look Darker than Dry Sand?
Wet one half of a brown paper towel with a damp sponge. Compare the wet part to the dry part. Which one looks darker? What happens as it dries?
41. Why Do Colors on a Phone Screen Look Different From Colors on Paper?
Choose a colorful photo on a screen, print or draw it, and compare the two side by side. Which colors look different? Move the paper under different lamps to see what changes.
Do this with a grown-up42. Why Are Roofs in Hot Places Often Painted White?
Wrap one jar in white paper and another in black paper. Put a thermometer in each (or hold your hand near them), set them in the sun for half an hour, and compare the readings.
43. Why Do Old Posters in Sunny Windows Fade to Blue?
Tape a strip of black paper over half of a colored sheet and leave it by a sunny window for a few weeks. Peel it off and compare the covered and uncovered parts.
44. Why Do Magicians Hang Black Cloth Behind Their Tricks?
Put a small toy on a sheet of white paper and another on black cloth, then take a photo of each. Which toy is easier to see? Try wrapping a toy in black cloth in front of a black background.
45. Why Can’t You Make Black by Mixing Colored Lights?
Stack red, green, and blue cellophane sheets on top of each other and hold them up to a window. How dark does it get as you add each sheet?
46. Why Do Newspaper Pictures Turn Into Tiny Dots Under a Magnifier?
Look at a color comic with a magnifying glass, and find the tiny dots. How many different colors of dots can you spot? Move the magnifier away and see the dots blend.
47. Why Can Bees See Patterns on Flowers That We Cannot?
On a sunny day, look closely at a flower and sketch any patterns you see, like stripes or rings. Then picture how a bee might see an extra ultraviolet pattern. Watch bees from a safe distance and never disturb them.
48. Why Does a Red Apple Look Almost Black Under a Green Light?
In a dark room, cover a flashlight with green cellophane. Shine it on a red object and a green object. Which one looks brighter? Then try red cellophane.
49. Why Do Artists Use a Color Wheel to Pick Colors That Look Good Together?
Draw a color wheel with twelve colors using paint or crayons. Find the opposite of each color, and try making a small picture that uses only neighbors, and another that uses only opposites.
50. Why Does Paint Change Color a Little as It Dries?
Paint a swatch of a color and snap a photo while wet. Check the same swatch when it is dry. Did it change? Try another type of paint, too.
Expedition 3: Mirrors, Lenses & Bending Light (25)
51. Why Can You See Yourself in a Mirror but Not in a Wall?
Hold a glossy magazine page and a plain sheet of paper at the same angle near a window. Which one shows a reflection of the window? Why do you think that is?
52. Why Does Light Bounce Off a Mirror at the Same Angle It Hits?
Lay a small mirror flat on a table, and shine a flashlight at it from the side. Can you aim the bounced beam at a target on the wall, like a sticky note?
53. Why Can a Periscope Let You See Over a Wall?
With a grown-up, build a periscope from a cardboard milk carton or a long box, with two small flat plastic mirrors tilted at 45 degrees. Look over a table’s edge to see what is behind it.
Do this with a grown-up54. Why Do Two Mirrors Facing Each Other Show Endless Copies?
Stand two unbreakable hand mirrors facing each other with a small toy between them. Count the copies. Then tilt them like an open book, and see how the number of copies changes. Ask a grown-up to handle any glass mirrors.
Do this with a grown-up55. Why Does Your Face Look Upside Down in the Back of a Spoon?
Look at your reflection in a clean spoon. Hold it at arm’s length and then close to your eye. Where does the picture flip, and where does it stay upright?
56. Why Do Car Side Mirrors Say Objects Are Closer than They Appear?
Compare a flat mirror to the back of a shiny spoon. Which one shows more of the room? In which one do objects look smaller?
57. Why Does a Makeup Mirror Make Your Face Look Bigger?
With a grown-up’s permission, look into a curved makeup mirror. Move slowly away from it. At what distance does your face turn upside down?
Do this with a grown-up58. Why Does a Swimming Pool Look Shallower than It Really Is?
Put a ruler in a clear tub of water, and look at it from the side. The part under water seems to jump upward. Remember: real pools are always deeper than they look, so never judge depth by looking.
59. Why Does a Coin Appear When You Pour Water Into a Bowl?
Place a coin in an empty bowl and step back until the rim just hides it. Keep your head still while a friend pours water in gently. Does the coin pop into view?
60. Why Does a Glass of Water Flip an Arrow Upside Down?
Draw an arrow on a card and hold it behind a tall clear glass of water. Slowly move the card away. At what distance does the arrow flip direction?
61. Why Does a Magnifying Glass Make Things Look Bigger?
Use a magnifying glass to look closely at a leaf, a feather, a coin, and your fingertip. Draw what you see. What small details appear that you could not spot before?
62. Why Should You Never Play with a Magnifying Glass in the Sun?
Use a magnifier only indoors to look at things, always pointing it away from windows and the Sun. Keep it in a case, and ask a grown-up where to store lenses so they never face the Sun.
Do this with a grown-up63. Why Do Some Lenses Make Things Look Smaller?
Look through a door’s peephole from the inside with a grown-up. How much of the hallway can you see, and how big do people look?
Do this with a grown-up64. Why Can a Water Drop on a Leaf Work Like a Tiny Lens?
Put a clear piece of plastic wrap over some small print. Use a dropper or a spoon to place one small water drop on it. Look through the drop. How much bigger do the letters look?
65. How Does a Microscope Show Things Too Small to See?
Look at a pinch of salt and a pinch of sugar with a magnifying glass. Draw the shapes of the crystals. Can you tell the two apart?
66. Why Is the Word Ambulance Written Backward on the Front of the Van?
Write your name backward on a piece of paper, letter by letter in reverse order. Then hold it up to a mirror. Can you read it? What happens with the letters that already look the same in the mirror?
67. Why Can You See Your Room Reflected in a Window at Night?
At night, look at a window from inside with the room lights on. Then switch off the lights, or cup your hands around your eyes against the glass. What changes? Do not go outside alone in the dark.
Do this with a grown-up68. Why Can Some Windows Look Like Mirrors From the Outside in the Daytime?
On a sunny day, look at a mirrored office window from outside and notice your reflection. If you get a chance, compare how it looks from inside. Which side seems more mirror-like?
Do this with a grown-up69. Why Does a Calm Lake Show a Mirror Picture and a Windy Lake Does Not?
After rain, find a still puddle and look at the reflection. Then drop a tiny pebble in and watch the reflection break up and slowly come back together.
70. Why Do Things Look Bigger and Closer Underwater?
Look at a toy through the side of a clear plastic tub filled with water. Then compare with the same toy outside the tub. Does it look bigger? Is it where you expected?
Do this with a grown-up71. Why Does a Lens Bring Light Together at One Spot?
Stand at a window (not facing the Sun), and hold a magnifying glass between the window and a sheet of paper. Move the paper back and forth until you see a small upside-down picture of the window.
72. Why Does a Kaleidoscope Make Endless Patterns?
With a grown-up, make a kaleidoscope by taping three small plastic mirrors in a triangle inside a cardboard tube, with a few colorful beads at one end. Turn it slowly and watch the patterns.
Do this with a grown-up73. Why Do Funhouse Mirrors Make You Look Wide or Skinny?
Crumple a piece of shiny foil, flatten it a little, and look at your face in it. Tilt it in different directions and watch your face stretch and squash.
74. Why Do You Only Need a Half-Length Mirror to See Your Whole Body?
Stick tape on a mirror at the places where you can see the top of your head and the tip of your toes. Step back and forward. Does the spacing change? Measure it. It should be half your height.
75. Why Do Shiny Round Balls Show the Whole Room in a Tiny Picture?
Look at a shiny kettle, a polished metal bowl, or a bike bell. Find your face and the windows or lamps around you. How much of the room fits in the reflection?
Do this with a grown-upExpedition 4: Shine, Matte & See-Through (25)
76. Why Can You See Through Glass but Not Through Wood?
Collect ten small objects, such as a spoon, a cup, a leaf, and a piece of plastic wrap. Sort them into two piles: “see-through” and “not see-through.” Test each one with a flashlight.
77. Why Does Frosted Glass Hide Shapes but Still Let Light In?
Put a piece of tape or wax paper over a clear window or a plastic sheet. Place a toy behind it and look from near and far. How does the toy look through it? What happens when the toy touches the sheet?
78. Why Does a Sheet of Paper Glow When You Hold a Flashlight Behind It?
In a dark room, shine a flashlight behind a sheet of white paper. Cut simple shapes out of a second paper and see how the glow changes. Keep paper away from hot bulbs.
Do this with a grown-up79. Why Does Wet Paper Turn See-Through?
Put one small drop of cooking oil on a piece of paper bag or paper towel. Hold it up to a window. What happens to the spot? Does it get lighter or darker?
Do this with a grown-up80. Why Are Some Things Shiny and Others Dull?
Compare a glossy sheet of paper, a matte sheet, a smooth plastic cup, and a sandy rock under a lamp. Sort them from shiniest to dullest. Which ones are smoothest to touch?
Do this with a grown-up81. Why Are Metals So Shiny?
Compare a metal spoon, a plastic spoon, a wooden spoon, and a piece of foil. Which ones show your face? Which show no reflection at all?
82. Why Does Polishing Make a Spoon Shinier?
With a grown-up, rub a dull copper coin with a soft cloth and a little lemon juice and salt. Rinse and dry it. Compare it with a coin you did not rub. Wash your hands afterward.
Do this with a grown-up83. Why Do Air Bubbles in Water Look Silvery?
Look at the bubbles in a glass of fizzy water or in a fish tank from the side. Notice their silver shine. Try different angles to see when the shine appears and disappears.
84. Why Does Frost Sparkle?
On a bright, frosty morning, look at the snow or frost and move your head slowly from side to side. Watch the sparkles blink on and off. Always wear a hat and sunglasses in bright snow.
85. Why Do Gemstones Sparkle More When They Are Cut?
Look at a cut-glass bowl or a clear plastic gem under a lamp. Turn it slowly. Count how many flashes you see. Then look at a smooth glass bead. Which one sparkles more?
Do this with a grown-up86. Why Do Glitter and Sequins Flash When You Move?
Sprinkle a little glitter on a sheet of paper under a lamp. Tilt the paper slowly. Watch which specks light up. Keep glitter away from your eyes and wash your hands after.
Do this with a grown-up87. Why Do CDs and DVDs Shimmer with Colors?
Hold an old, uncracked CD by the edges under a lamp and tilt it slowly. Which colors appear and where? Never hold it in direct sunlight or point the reflection at anyone’s eyes.
Do this with a grown-up88. Why Does the Inside of a Seashell Shimmer with Colors?
Look at the inside of a seashell or a pearly button under a lamp. Tilt it slowly. How many different colors can you find? Do they change as you move your head?
Do this with a grown-up89. Why Does a Wet Leaf Look Shinier than a Dry One?
Pick up a few leaves or stones. Compare one dry and one wet. Which looks shinier? Which looks darker? Try wiping one dry and watch the shine disappear.
90. Why Does Glare Make a Shiny Page Hard to Read?
Read a glossy magazine page under a lamp. Tilt the page until you see glare, then tilt it back until the words are clear. Try moving the lamp to one side.
Do this with a grown-up91. Why Do Phone Screens Turn Into Mirrors in Bright Sunshine?
Look at a screen near a sunny window and move it around. Find where the glare is worst and where it is gone. Try shading it with your hand. Never look directly at the Sun.
92. Why Can a Pond Look Like a Mirror When You Look From Low Down?
From a safe spot away from the edge, look at a puddle, a pond, or a pool from high up, then crouch low. At which height do you see the sky’s reflection most clearly?
93. Why Is Muddy Water Cloudy?
Stir a spoonful of soil into a clear jar of water, and shine a flashlight through it from the side. Watch the water clear up as the dirt settles. How long does it take?
94. Why Does Milk Look White When Water Is Clear?
Add one drop of milk to a glass of water and shine a flashlight through it from the side. Add a few more drops and notice how white it becomes.
95. Why Is the Foam on a Dark Drink White?
Pour some dark juice into a glass. With a grown-up’s help, blow bubbles into it with a straw (blow, don’t suck). Look at the white foam on top. What color is the liquid underneath?
Do this with a grown-up96. Why Is Table Salt White When One Crystal Is Clear?
Look at a grain of coarse salt, a sugar cube, and a piece of rock candy with a magnifying glass. Which crystals are clear? Why does the sugar cube look white?
97. Why Are Some Plastics Clear and Others Cloudy?
Collect different plastic containers from the recycling bin (washed). Hold each one up to a window. Sort them into clear, a little cloudy, and very cloudy. What do the cloudy ones have in common?
98. Why Do Some Windows Have a Thin, Shiny Coating?
With a grown-up, shine a small flashlight at an angle on a double-pane window in a dim room. Look for several faint reflections. Do any look slightly colored?
Do this with a grown-up99. Why Does Crinkled Foil Sparkle in Every Direction?
Smooth half of a piece of foil and wrinkle the other half. Hold it under a lamp. Which half shows a clear reflection? Which half sparkles? Be careful of the foil’s sharp edges.
Do this with a grown-up100. Why Do Very Dark Materials Like Velvet Seem to Swallow Light?
Compare black velvet, black paper, and black plastic under a lamp. Which one reflects the most light? Which looks darkest? Try taking photos of each.
Do this with a grown-upExpedition 5: Light Machines & Tricks (25)
101. Why Does a Laser Pointer Make a Tiny Dot Instead of a Wide Beam?
With a grown-up in charge, compare a flashlight and a laser pointer shone at a wall from the same distance. Only the grown-up handles the laser, and it points only at the wall, never at anyone.
Do this with a grown-up102. Why Must You Never Shine a Laser Pointer at Anyone's Eyes, a Plane, or an Animal?
Make a poster that says “Lasers are tools, not toys” and lists three safety rules. Put it on your wall or at school. If you ever find a laser pointer, give it to a grown-up.
Do this with a grown-up103. Why Does a Projector Turn a Tiny Picture Into a Huge One?
With a grown-up, put a phone with a bright picture in a cup or shoebox, and place a magnifying glass in front of it. Move the box until a big, upside-down picture appears on a dim wall.
Do this with a grown-up104. Why Does a Flip Book Make Pictures Move?
Draw a stick figure in the corner of twenty pages of a small notepad, changing it slightly each time, like a ball bouncing. Flip the pages with your thumb. Does it look like it moves?
105. Why Do Hologram Stickers Change as You Tilt Them?
Look at a hologram sticker under a lamp and tilt it. Which colors do you see? Does the picture seem to float or change depth? Ask a grown-up to show you one, and look but don’t scratch it.
Do this with a grown-up106. How Do Optical Fibers Trap Light Inside a Thread?
Over a sink, a grown-up pokes a small hole near the bottom of a clear plastic bottle. Fill it with water, shine a flashlight into the back in a dim room, and watch the light follow the water stream as it curves.
Do this with a grown-up107. What Is Infrared Light, and Why Can We Feel It but Not See It?
Point a TV remote at a phone camera (with a grown-up’s permission), press a button, and look at the screen. Do you see a faint purple flash? Your eyes could not see it.
Do this with a grown-up108. Why Do Streetlights Switch on by Themselves at Dusk?
Cover the solar panel of a garden light with a paper cup in the daytime. Does the light turn on after a minute? Take the cup off and watch it switch off.
109. How Does a Solar-Powered Calculator Work Without a Battery?
Cover the solar strip on a solar-powered calculator with your finger, then with paper. Watch the numbers fade. Uncover it and see them return. Try it under different lights.
110. Why Can One Tiny LED Shine Red, Green, or Blue?
Spot all the LED lights around you, like those on a remote, a charger, or a toy. How many different colors can you find? Ask a grown-up to show you a color-changing LED lamp.
Do this with a grown-up111. Why Does a Flashlight Beam Get Wider the Farther It Goes?
Shine a flashlight at a wall from one step away, then three steps, then six. Trace each circle with chalk on paper, or stick small notes at the edges. How does the size change?
112. Why Does a Flashlight Have a Shiny Cup Behind the Bulb?
Cup a piece of foil behind a small LED keychain light, and shine it at the wall. How does the beam change? Try moving the foil closer or farther from the light.
113. Why Does a Mirror Ball Scatter Dots of Light Around a Room?
Hang a small piece of foil-covered cardboard from a string near a lamp, and let it spin. Watch the light dots dance on the walls. Which direction do the dots travel compared with the cardboard?
Do this with a grown-up114. Why Do 3-D Glasses Make Pictures Seem to Pop Out?
Hold a pencil at arm’s length in one hand, and a second pencil in the other hand. Close one eye and try to touch the tips together. Then try with both eyes. Which is easier?
115. Why Do Some Screens Go Dark When You Tilt Polarized Glasses?
With a grown-up’s permission, look at a calculator or monitor through polarized sunglasses. Slowly tilt your head sideways, or rotate the glasses. At what angle does the screen go dark?
Do this with a grown-up116. Why Do Magicians' Mirror Tricks Fool Our Eyes?
Stand a small mirror at a slant inside an open box so it reflects the inside wall. Hide a toy behind the mirror. Look from the front. Can your friend find where the toy is hiding?
117. Why Does the Same Line Look Longer with Arrowheads on the Ends?
Draw two lines of the same length, one with arrowheads pointing inward and one with them pointing outward. Ask a friend which is longer, then measure with a ruler. Who was fooled?
118. Why Can a Laser Measure How Far Away a Wall Is?
Ask a grown-up to use a laser measure to find the width of a room (aimed only at the wall, never at a person). Then measure the same distance with a tape. How close are the answers?
Do this with a grown-up119. Why Can a Scanner Copy a Picture Using a Moving Line of Light?
With a grown-up, scan a drawing and a blank sheet of paper. Watch the light bar move. Does the scanned picture look like your drawing? Try scanning a leaf, too.
Do this with a grown-up120. Why Do Indoor Plant Lamps Often Look Pink or Purple?
Plant cress seeds in two cups of damp soil. Put one on a sunny windowsill and one in a dark cupboard. Check them for five days. How do the plants differ?
121. Why Do Some Solar Power Plants Use Hundreds of Mirrors?
With a grown-up, use a small mirror to bounce sunlight onto a shaded wall. Can you add another mirror to make the spot brighter? Never aim sunlight at a person, a window, or a driver.
Do this with a grown-up122. Why Does a Lamp Look Dimmer the Farther Away It Is?
At dusk, with a grown-up, have a friend walk away from you holding a flashlight. How does the light change as they go? At how many steps can you barely see it?
Do this with a grown-up123. Why Can a Laser Read the Tiny Bumps on a Disc?
Hold an old CD and an old DVD under a lamp and tilt each. Which one has finer rainbow lines? Which has more rows packed together? Handle them by the edges.
Do this with a grown-up124. Why Do Neon Signs Glow?
On a walk with a grown-up, look for glowing signs. Which ones look like neon tubes and which look like LEDs? Which have the orange-red glow of pure neon?
Do this with a grown-up125. How Can a Small Mirror Flash a Signal Across a Valley?
With a grown-up, use a small mirror to flash sunlight onto a far wall in a shaded area. Try to hit a target on the wall. Never flash it at people, cars, or windows.
Do this with a grown-upExpedition 6: Lamps, Lights & Safe Looking (25)
126. Why Do Bike Reflectors Shine When a Car's Headlights Hit Them?
At dusk, with a grown-up in a safe yard, shine a flashlight at a bike reflector from different angles. Stand next to the flashlight. Does the reflector glow back toward you each time?
Do this with a grown-up127. Why Do Crossing Guards and Road Workers Wear Bright Vests?
In a safe yard with a grown-up at dusk, hold up a dark jacket and a reflective strip. Shine a flashlight on both from far away. Which one can you see from farther?
Do this with a grown-up128. Why Do Bikes Need a White Light in Front and a Red Light in Back?
With a grown-up, check your bike. Is there a white front light, a red rear light, and reflectors? Test that the batteries work. If a light is missing, ask a grown-up to help you fix it before riding at night.
Do this with a grown-up129. Why Does a Flashlight Look Weaker in Fog or Rain?
In a dim room, spray a fine mist from a spray bottle into the air and shine a flashlight through it. See how the beam lights up. Compare it with a beam in clear air.
130. Why Do Some Lamps Look Warm and Yellow While Others Look Cool and White?
With a grown-up, check the labels on a few bulbs and find words like “warm white” or “daylight.” Look at white paper under each one. Which looks more yellowish and which looks bluer?
Do this with a grown-up131. Why Does a Flashlight Get Dimmer as Its Batteries Run Down?
With a grown-up, compare two identical flashlights, one with fresh batteries and one with old ones. Which is dimmer? Never mix old and new batteries, and ask a grown-up to recycle dead ones.
Do this with a grown-up132. Why Is It Easier to Read When a Lamp Shines on the Page?
Read a page in a dim room. Move a lamp to different spots: behind you, beside you, and in front of you. Which spot makes the words easiest to read, and why?
Do this with a grown-up133. Why Should You Never Look Straight Into Very Bright Lights?
Make a list of five very bright things we should never stare at, such as the Sun and lasers. Practice looking away and shielding your eyes with your hand. Share the list with your family.
134. Why Do Night-Lights Stay Dim on Purpose?
In a dark room, switch on a night-light and wait a few minutes for your eyes to adjust. How many things can you see? Switch on a bright lamp and notice what changes.
Do this with a grown-up135. Why Do Exit Signs Stay Lit Even When the Power Goes Out?
Next time you are in a school, library, or store, find the nearest exit sign. Look for other ones along the way. Draw a simple map of your home showing the safest way out.
136. Why Do Drivers Switch Off Their High Beams for Oncoming Cars?
Next time you ride in a car at night with a grown-up, watch how the driver dims the lights when another car comes. Can you notice the glare when a car with bright lights goes by?
Do this with a grown-up137. Why Do Airplanes and Boats Have Red and Green Lights?
Draw a boat from above, with a red light on its left side and a green light on its right. Then draw the lights you would see if it were crossing in front of you.
138. Why Do Tall Towers Have Blinking Red Lights?
With a grown-up, find a tower, a tall building, or a wind turbine with a red blinking light at dusk. Use a clock to time how long between flashes. Is the timing always the same?
Do this with a grown-up139. Why Are Tunnels Extra Bright Near the Entrance?
Step from bright sunshine into a dim room with a grown-up. Count how many seconds it takes until you can see things clearly. Do you see better after a minute?
Do this with a grown-up140. Why Do Window Blinds Control How Much Light Comes In?
Ask a grown-up to tilt the blinds at different angles while you watch the patch of light on the floor. How does it change? Keep blind cords out of reach and let only grown-ups handle them.
Do this with a grown-up141. Why Do Lamps Have Shades?
With a grown-up, use a cool LED lamp and compare how it looks with and without a paper shade. Keep paper and cloth away from hot bulbs. Which version is easier on your eyes?
Do this with a grown-up142. What Is Ultraviolet Light, and Why Can't We See It?
With a grown-up, put UV-sensitive craft beads outside in the sun and watch them change color. Then move them into the shade or indoors. How long does it take for the color to change back?
Do this with a grown-up143. Why Are Special Eclipse Glasses Safe When Ordinary Sunglasses Are Not?
Ask a grown-up to check that any eclipse glasses have the ISO 12312-2 mark and no scratches. Never look at the Sun with anything else. Or make a pinhole viewer with a card and look at the picture on the ground.
Do this with a grown-up144. Why Are Old Paintings and Photographs Kept in Dim Light?
Next time you visit a museum or gallery, notice how bright each room is and which artworks are in dim corners or behind curtains. Why do you think those ones are kept dimmer?
145. Why Are Brake Lights Red?
From a safe spot on the sidewalk, with a grown-up, watch cars from behind as they slow down. Can you tell the difference between tail lights and brake lights?
Do this with a grown-up146. Why Do Emergency Vehicles Flash Red and Blue Lights?
Make a short list of what you should do when you see or hear an emergency vehicle (for example, stop and stay away from the road, or pull over on a bike). Share it with your family.
147. Why Should You Keep Paper and Curtains Away From Hot Lamps?
With a grown-up, walk around your home and look at each lamp. Is anything flammable close to a bulb? Move it away, and check that each lamp has the right bulb size.
Do this with a grown-up148. Why Can You See a Line of Light Under a Closed Door?
In a dim room, close the door with a lamp on in the hall. Watch the line of light, and notice what happens to it when someone stands or walks near the door.
Do this with a grown-up149. Why Do Some Athletes Put Dark Marks Under Their Eyes?
On a sunny day, look at a bright surface, like a sidewalk, with and without a cap brim or your hand shading your eyes. Which makes it easier to see? Never look at the Sun.
150. What Is Light Really Made Of?
Tie one end of a long rope or jump rope to a doorknob, and flick the other end to send a wave along it. Make slow waves and fast waves. Light waves are like this, but far, far faster and much smaller.