"This activity models how tensional forces can cause fractures in rocks, sometimes creating rift valleys" From description of youtube
The earth is a dynamic planet, in ours human life time we barely note that, perhaps just when a volcano erupt or a earthquake destroys a city. Analyzing geological features in rocks we found out pieces of a huge puzzle and then theories are created. To confirm those theories some lab experiments were made. This video shows a qualitative experiment that demonstrates how normal faults are formed in a rifting process.