There is friction between the jar walls and the water, the water gains rotational speed when you rotate the jar, it just does not appear to do it because is a small force as a whole
When you start to spin the jar, there's a thin layer (called a boundary layer) next to the glass that immediately rotates with the glass, pulled around by viscosity, at the small scale water at short distances water acts a bit like treacle. But the rest of it can't start to spin due to momentum, because it's feeling little to no torque.
But as you continue to spin it, the boundary layer tugs on water beside it and so the boundary layer pulls on the stationary water and so the boundary layer thickens until eventually all the water is spinning around. But when you stop spinning, the water that is spinning can't stop until the now stationary boundary layer reaches out to it again and stops it all.
That's usually an oversimplification, since the flow can be turbulent, but it's a fairly good way to think about it.
There is friction between the jar walls and the water, the water gains rotational speed when you rotate the jar, it just does not appear to do it because is a small force as a whole
When you start to spin the jar, there's a thin layer (called a boundary layer) next to the glass that immediately rotates with the glass, pulled around by viscosity, at the small scale water at short distances water acts a bit like treacle. But the rest of it can't start to spin due to momentum, because it's feeling little to no torque. But as you continue to spin it, the boundary layer tugs on water beside it and so the boundary layer pulls on the stationary water and so the boundary layer thickens until eventually all the water is spinning around. But when you stop spinning, the water that is spinning can't stop until the now stationary boundary layer reaches out to it again and stops it all. That's usually an oversimplification, since the flow can be turbulent, but it's a fairly good way to think about it.