Strain tensor

A strain tensor is a fancy way of measuring how much something gets stretched or squished. Imagine holding a rubber band, and then pulling on both ends. The farther you pull, the longer the rubber band gets. This stretching is called strain.

Now, imagine doing the same thing with a piece of clay. Instead of getting longer, the clay gets thinner and wider. This squishing is also called strain.

A strain tensor helps us measure how much the rubber band or clay has changed shape. It has lots of little numbers that help us figure out exactly how much stretching or squishing is happening in different directions. This can be really helpful for things like building bridges or designing space shuttles, because we need to know how materials will behave when they are under stress.