Thermal Expansion
Ball and ring demo.
A metal ball JUST barely fits through a metal ring at room temperature. You heat the ball with a torch until it's red-hot.
What happens when you try to push the hot ball through the ring?
The hot ball doesn't fit! Metals expand when heated. But here's the twist — heat the ring too, and the ball fits again!
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Heat the ball, then try the ring. Now heat both — the ball fits again! The hole expands just like a solid disk would.
ΔL = αLΔT
Everything scales proportionally — including holes, gaps, and spaces
Bridges have gaps to accommodate thermal expansion — without them, they'd buckle in summer
Rails have small gaps that close in hot weather — old tracks buckled without them
Fillings must match the tooth's expansion rate — mismatch causes cracking
“Heat makes everything bigger — even the holes.”
Expansion Lab
Heat different materials and watch them expand. Compare expansion rates and explore the ball-and-ring puzzle.
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Try heating a bimetallic strip — two metals bonded together with different α values. Watch it BEND! This is how old thermostats work.
The expansion coefficient α differs by material: aluminum expands 2× more than steel. This mismatch creates forces — useful in thermostats, destructive in engineering.