# Real World Physics Situation Requires Theory and Insight

1. Oct 21, 2009

### stantz

Hello.

I hope I am posting in the right section, apologies if I am not.

I need help with a situation that has arisen for a colleague of mine, he asked me for help but sadly I cant give him an answer based on fact and logic. Can you please help?

In his kitchen he has a glass panel which is about 2 meters wide, by 1 meter high.

This panel has a hole in the centre where a plug socket is located. His kitchen stove is under the panel to the left. The stove is electric, and has malfunctioned and when the main oven switch is set to on it automatically sets the back hob to the highest heat.

The glass has cracked at the plug socket, to the right of the socket. The crack was not witnessed, and occurred during the night when the oven was off but most likely used that same night.

Could the heat cause the crack?

He was told by an engineer (electrical) who came to fix the oven that the malfunction could not cause the crack as it was not directly over the hob, but the glass has an obvious weak point in the centre. Could excess heat and then cooling cause this to happen away from the left hand side of the glass where the hob is located, making the crack appear next to the week point of the hole?

It will be great to hear your thoughts and feedback regarding this, I look forward to it.

Regards,

Ray.

PS> The glass is frosted, about 1cm thick and mounted against the wall.

2. Oct 21, 2009

### Mapes

It is true that temperature changes cause materials to expand and contract, and can thus causes internal stresses if an object is constrained. It's also true that stress is concentrated at holes, corners, and other areas of high curvature, and it's in these areas that failure often initiates. So I think your hypothesis is reasonable. You can read more about these topics in mechanics of materials textbooks (like Dowling, Courtney, or Beer and Johnston).