Snapping in Physics

We slowly changed the amount we bent the pencil, but it broke abruptly in a snap. Many things make abrupt transitions when we change them slowly:

• Like pencils, glass windows and airplane wings crack when you change the amount of bending.
• Electric light switches, as you change their angle, go abruptly from OFF to ON.
• As you slowly change the temperature, ice melts abruptly at 32 degrees F (zero degrees C). (The ice melts slowly as you add heat, but the temperature doesn't change until all the ice has melted. Try it!)

Here is our computer model, showing a SNAP. We'll talk more about this model when we start studying crackling noise in magnets.

Above, you see a colored blob take over the black region. Maybe a couple of small blobs happen first, but then a big one sweeps over the black region. Does it look a tiny bit like black ice melting? Or a very slow crack going through a pencil?

Our model is not a very good model of either melting ice or pencils breaking, but it shows exactly what we mean by a snap.