Why questions, answered with pictures

• Why is the sky blue?: Sunlight scatters off air molecules, and blue scatters far more than red. See it happen in an interactive picture, then go three levels deeper.
• Why do we have seasons?: It's Earth's tilt, not its distance from the Sun. An interactive picture shows how the same sunlight spreads out in winter.
• Why does the Moon change shape?: The Sun always lights half of the Moon. As it circles Earth we see more or less of that lit half. Watch the phases in an interactive picture.
• How does photosynthesis work?: A leaf turns water, carbon dioxide and sunlight into sugar and oxygen. See the inputs and outputs move in an interactive picture.
• Why can't you divide by zero?: Division asks how many groups fit. Groups of zero never add up to anything. See why in an interactive picture with apples.
• The Pythagorean theorem, shown with squares: On a right triangle, the squares on the two short sides fill the square on the long side exactly. See a² + b² = c² in an interactive picture.
• Why do a triangle's angles add up to 180°?: Tear off the three corners of any triangle and they line up into a straight line. See it in an interactive picture.
• What does 3/4 actually mean?: A fraction counts equal parts of a whole. See three quarters as a pizza and as a bar in an interactive picture.
• Why is the sea salty?: Rain wears salt out of rocks, rivers carry it to the sea, and evaporation leaves it behind. See the whole cycle in an interactive picture.
• Why do leaves change colour in autumn?: The yellows were there all along, hidden by green chlorophyll. See the green fade in an interactive picture.
• How does a lever make lifting easier?: Push far from the pivot and a small force lifts a big load. See the balance of force and distance in an interactive picture.
• What is a derivative?: A derivative is how fast something changes at one instant: the slope of a curve at a point. See a line become a tangent in an interactive picture.
• The Why tho? button: keep asking until it clicks: Under every answer, one tap goes a level deeper into the reason behind it, until the idea bottoms out. Here's how it works.
• Guess first: why Why Tho? asks before it explains: Before showing you the answer, Why Tho? asks what you already think. Here's why a quick guess makes learning stick.
• Pictures drawn for your question: When words aren't enough, Why Tho? draws a short interactive picture of the idea, written as code and checked before you see it.
• Teach it back: the best test of understanding: Flip the roles: you explain the idea, and Why Tho? plays a curious beginner whose questions find the gaps.
• Practice sheets made from your own chat: One tap turns what you just learned into a short practice sheet: do it on screen, where it checks itself, or print it.
• Your tree of thoughts: Everything you learn grows a tree: a trunk of maths and science, with branches for everything else you're curious about.
• Homework help that never just hands over the answer: Bring a homework problem and Why Tho? guides you to solve it yourself, one step at a time. Here's why that's the point.
• Why Tho? for parents: approval, progress and privacy: Why Tho? is for ages 13 and up. Under 18, a parent approves first. Parents see progress and weekly summaries, never the chats.
• Learn in English, French or Spanish, your way: Why Tho? speaks English, French and Spanish, and lets you pick an easier-to-read font, bigger text, dark mode and read-aloud.