Looking at famous cathedrals like Notre-Dame and Chartres helps us understand how they stay strong and elegant. Here are some key points about their design and structure:

1. Smart Design Choices:

   • Flying Buttresses: These cool supports stick out from the walls. They help hold up the building, spreading out the pressure so the walls can be taller and stronger.
   • Sharing the Load: The weight of the building is shared evenly by the columns and arches, which helps keep everything stable.

2. Materials Matter:

   • Heavy Stone: The granite used in these cathedrals is really heavy, weighing around 2,750 kg per cubic meter. This weight affects how stable the building is.
   • Strong Arches: Arches are awesome! They can support more weight than they actually weigh themselves, thanks to their curved shape that helps shift the pressure.

3. Understanding Stability:

   • In Notre-Dame, the main area, called the nave, deals with a strong compressive force from the roof. This force is about 15,000 Newtons per square meter.
   • Events like the fire in 2019 show us how important it is for these buildings to keep the balance of forces. When that balance is off, problems can happen.

These examples show just how carefully these cathedrals were built to stay standing for many years!