The
Science
of Media
Every photo is light that bounced off something and travelled into a lens. Every song is air vibrating. Every video is a trick your brain plays on itself. This module explains the physics and biology behind the media you use, with experiments you can do at the kitchen table.
- 00First Principlesp.2
- 01Light & opticsp.4
- 02Eyes & camerasp.5
- 03The science of colourp.6
- 04Sound & digital audiop.7
- 05Why still frames look like motionp.8
- ✦Self-check · Make it · 5 Questions · Side Questp.9
You'll need: pencil, calculator, a phone, a clear glass of water, a straw, a spoon, a cardboard box, foil, a pin, a lamp, a rubber band and some card.
Principles
A first principle is a basic truth you can build on. Cameras, screens and speakers can seem like magic boxes, but they all run on a few rules of physics and biology. Three questions to start. Be honest; nobody's grading this.
What do I already know?
What is necessary?
Everything in this module is built from four bricks. Rate yourself on each one, then check the example to see if your rating holds up.
What is the objective?
By the end, you'll be able to explain the science that turns light and sound into media.
- 01Explain reflection, refraction and how a lens focuses light.
- 02Compare how an eye and a camera capture an image.
- 03Explain additive (RGB) and subtractive (CMYK) colour.
- 04Describe sound as a wave and calculate digital audio sizes.
- 05Explain why fast still images look like motion.
- 06Light a scene on purpose using three lights.
The list on the left is ours. Now make it yours. What do you want out of this?
How much do you know about the science behind media right now? Shade the boxes in pencil. You'll come back at the end (p.9) and shade it again in pen.
Why start this way? When you know what you already have (1), what you need (2) and where you're going (3), you learn faster and you notice the gaps. Every module on the Media Path starts with these same three questions.
Light bends the rules
Light travels about 300,000 km every second. Everything you see is light that bounced off something and landed in your eye or a camera. On the way, it can bounce, bend and be focused.
How far away is that lightning?
Light reaches you almost instantly. Sound is much slower: about 343 metres per second in air at 20 °C.
Shortcut: every 3 seconds is about 1 km. And if you can hear thunder, head indoors.
Bend it, flip it
1. Put a straw in a clear glass of water and look from the side. What happens to the straw at the waterline?
2. Look at your face in the bowl of a spoon, then the back. Which side flips you upside down?
The Sun is about 150,000,000 km away. Light travels about 300,000 km/s. How long does sunlight take to reach you? Give your answer in minutes and seconds. What about light from the Moon (about 384,400 km away)?
Your eye is a camera
Eyes and cameras solve the same problem the same way: an opening lets light in, a lens focuses it, and a light-sensitive surface records it.
| Job | In your eye | In a camera |
|---|---|---|
| Control how much light gets in | Iris and pupil | Aperture |
| Focus the light | Lens (and cornea) | Lens |
| Record the image | Retina: roughly 90–120 million rods (dim light) and 4–6 million cones (colour) | Image sensor (more in Lens 4) |
A camera's shutter speed is how long the sensor collects light. A car moving at 20 m/s:
Fast shutter freezes action. Slow shutter makes motion blur, which can look cool on purpose.
Look in a mirror in a bright room. Cover your eyes with your hands for 15 seconds, then uncover them and watch your pupils closely. What happens, and why would your eye do that?
Never look at the Sun, directly or through any lens.
Aperture is written as an f-number like f/2 or f/4. Smaller number = bigger opening. The light let in depends on 1 ÷ (f-number)². How many times more light does f/2 let in than f/4? Than f/8?
Two kinds of colour
White light is a mix of many wavelengths. Your eyes see roughly 380 to 700 nanometres, from violet to red. An apple looks red because it reflects mostly red light and absorbs the rest.
Screens add light. Red + green = yellow. All three = white. No light = black.
Ink absorbs (subtracts) light. Cyan + yellow = green. All three ≈ dark, so printers add K (black).
Web colours are written like #FF8800: two digits each for red, green and blue, in base 16.
Put one tiny drop of water on your phone screen over a white area (or use a magnifying glass). The drop acts like a lens. What colours do you see? Wipe it off after.
Isaac Newton used a prism in the 1660s to show white light splits into a spectrum. Now find out: why is the sky blue, and why are sunsets orange? (Search "Rayleigh scattering.") Explain it in two sentences anyone could follow.
Sound is a wave
Sound is a vibration that travels through air as waves of pressure. Frequency (how many waves per second, in hertz, Hz) sets the pitch. Amplitude (how big the waves are) sets the loudness.
Humans hear roughly 20 Hz to 20,000 Hz (the top end drops as you age). To record sound digitally, a microphone turns air pressure into electricity, and a computer measures it thousands of times a second. Each measurement is a sample.
CD audio takes 44,100 samples per second, each stored with 16 bits, in 2 channels (stereo).
Hold a ruler flat on a table edge with part of it hanging off. Flick the end. Now slide it so less hangs off and flick again. What happens to the pitch? Why? (Think: how fast is it vibrating?)
To capture a frequency, you need to sample at least twice as fast as it vibrates (the Nyquist rule). What's the highest frequency 44,100 samples/s can capture? Is that above human hearing? Also: how many loudness levels does 16 bits give (216)?
How stills become motion
Video is just still pictures. So why do they look like they're moving? For a long time people credited "persistence of vision", the idea that images linger on the retina. Scientists now see that as an incomplete explanation: your brain actively fills in the motion between images.
Two effects matter. Apparent motion: when images change fast, your brain reads them as one thing moving. In 1912, psychologist Max Wertheimer studied a version called the phi phenomenon. And flicker fusion: a light flashing fast enough looks steady.
People played with this long before film. In the 1800s, optical toys like the thaumatrope (above), the phenakistiscope and the zoetrope made drawings appear to move.
At 24 fps, a dark gap between frames would flicker badly. Many film projectors used a shutter that flashed each frame twice (or three times).
Same 24 pictures, but the faster flashing fools your flicker detector.
Cut a card circle. Draw a bird on one side and a cage on the other (draw the cage upside down so it lines up). Tape it to a pencil and spin it fast between your palms. Then invent your own pair.
On video, spinning wheels sometimes look frozen or backwards. A wheel has 10 evenly spaced spokes and spins 2.4 times per second, filmed at 24 fps. How far does it turn between frames? Why might it look like it's standing still?
Quick self-check
Six questions, covering every stop. Show your thinking. Answers are upside down at the bottom; no peeking till you're done.
1 · You count 9 seconds between lightning and thunder. About how far away is it?
2 · Which part of a camera does the same job as your pupil?
3 · What colour do red and green light make together?
4 · What colour do cyan and yellow ink make together?
5 · A sound wave vibrates 440 times a second. What is its frequency?
6 · Film at 24 fps with a two-blade shutter flashes how many times per second?
Re-shade your knowledge meter
How much do you know about the science behind media now? Flip back to p.3 and shade the meter again in pen (or shade this one). Did any of the four bricks on p.2 move from "Not yet" to "Got it"?
Light it three ways
Filmmakers often light a subject with three lights: a key (main light), a fill (softens shadows) and a back light (separates the subject from the background). Try it with lamps from around your home, and photograph the difference.
1 · Set up
Pick a subject (a friend's face, a plant, a toy). Use lamps you already have. Sketch your setup from above:
2 · Shoot three versions
| Shot | Lights | What changed? |
|---|---|---|
| A | Key light only (one lamp, off to one side) | |
| B | Key + fill (a softer light or white card on the other side) | |
| C | Key + fill + back light (behind the subject) |
3 · Must-haves
- Same subject and camera position for all three
- One photo where the light feels scary, one where it feels warm
- Labels on each photo: which lights were on
- A one-line caption saying which version you like best, and why
4 · Explain the science
Why does moving the light change the shadows? Use the words straight lines and reflection.
Safety: lamps and bulbs get hot, so keep them away from fabric and paper, and let them cool before moving them. Ask permission before photographing anyone.
5 Questions
I Still Have
This module didn't answer everything. Good. Write 5 new questions it didn't answer, one of each type below. There are no wrong questions, only ones nobody's asked yet.
★ Star the one question you'd most like answered. You'll need it on the next page.
1What I'll find out
Break your big question into 2 or 3 smaller ones you could actually answer.
2Where I'll look
3How I'll share it
Who I'll share it with:
Done by: