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Why popcorn pops, and why some kernels never do
A popcorn kernel is a tiny, sealed pressure vessel. Its hard shell traps water inside the starchy core until heat turns that water to steam, and pressure…
Why a rainbow is always a circle 42° around your shadow
Every rainbow is part of a circle centred on the shadow of your head, with its red edge about 42° away. That number comes from inside a single raindrop…