First, we introduce a wood stick in a plastic glass and we cover it with dry sand.
We take out the stick without any problem
Then, we introduce the stick in the glass again, we cover it with dry sand again, and before picking it out, we beat the glass.
When we beat the glass, we can see that compression is higher
The particles are rearranged and the total volume and the empty space between the grains decrease.
In this case, the friction between particles increases and drag coefficient prevents we can take the stick out from the sand.
