Why
Principles
Why things work the way they do — the principle behind the phenomenon.
Why Is Ice Slippery?Ice isn't slippery because of melted water or pressure. A quasi-liquid layer, where surface molecules vibrate freely, coats the ice even below freezing and makes it slide.
Why Does a Mirror Reverse Left and Right?A mirror reverses neither left-right nor up-down. Only front-back (the z-axis). "Left-right reversal" is an illusion born from mentally rotating the image to face us.
Why Is a Rainbow Arc-Shaped?A rainbow is not an object in space but a cross-section of a 42° cone centered on you. That is why it is an arc, why it moves with you, and why your neighbor sees a different rainbow.
Why Does Soap Remove Grease?A soap molecule has a head that loves water and a tail that loves oil. The tails wrap grease into a micelle that rinses away whole. Soap is a bridge between water and oil.
Why Cola and Mentos EruptDrop a Mentos into cola and a fountain erupts. Not chemistry but physics: the candy’s microscopic roughness offers thousands of nucleation sites at once, releasing dissolved CO2 explosively.
Why Lightning Zigzags Instead of Going StraightLightning zigzags because air is an insulator and charge cannot flow straight. A step leader jumps in 50-meter steps, each toward the most easily ionized air, so the path bends.
Why an Everyday Electric Car Can Rival a Supercar Off the LineA launch is decided by torque, not horsepower. At zero rpm horsepower is meaningless, yet an electric motor gives full torque instantly. So for similar power, and often against a combustion car in the same price range, the electric car pulls ahead off the line. Top speed and sustained high-speed driving are a separate story.
Why Do Airplanes Fly?Airplanes don't fly on Bernoulli alone. The wing turns airflow downward and is lifted by the reaction, with angle of attack and curvature as the two knobs controlling that turning.
Why does wet paper tear so easily, while wet cloth gets tougher?Paper and cloth are both made of cellulose. Yet wet paper weakens while wet cloth grows stronger. The difference is not the material but where the strength comes from: bonds between fibers, or the way the fibers are tangled.
Why doesn't cutting split the atoms?Cut something with a knife and it feels as if the atoms inside are split, but what actually parts is not the atoms themselves but the connections between atom and atom. A blade is incomparably larger than an atom and cannot cleave one; it only pries apart the weaker connections. Splitting an atom's nucleus is a wholly different realm that takes enormous energy.