Most people who've watched a glazier work assume the tool is actually slicing through the glass. It isn't. This video from TTM-III unpacks the counterintuitive physics of what's really happening when a small carbide or diamond wheel rolls across a pane — and why the resulting break is so clean.

The core insight is that scoring is not cutting. The wheel creates a microscopic groove — a fissure only a few microns deep — but that groove acts as a stress concentrator. When the glazier applies a bending force, the entire tensile load of the sheet focuses at the tip of that tiny crack. Glass, being brittle and lacking the plasticity of metal, has no mechanism to blunt the crack tip, so it propagates cleanly and almost instantly along the score line.

What makes this worth watching beyond the party-trick appeal is that it's a tangible demonstration of fracture mechanics — the same principles that explain why airplane windows are round, why a scratched windshield eventually fails, and why the Liberty Bell cracked. It's a small channel doing a genuinely educational job of turning an everyday process into a physics lesson.