A pail filled with water of mass m is whirled in a vertical circle of radius , r . When the pail is at its highest point , its speed is v and the normal reaction of the pail on the water is R . Water does not fall out because ??

i know i am supposed to this :

$\displaystyle R+mg=\frac{mv^2}{r}$ so $\displaystyle R=\frac{mv^2}{r}-mg >0 $

$\displaystyle \frac{mv^2}{r}>mg$

It is because the centripetal force is greater than the gravitational acceleration ??If that's the case , water would spill up since F is downwards .

Why R+mg ?? When i draw the diagram , my R is pointing upwards and mg is pointing downwards and if the acceleration is downwards , shouldn't it be mg-R=ma ??

And why must R be greater than 0 and not other values ??

I really appreciate ur effort to explain this to me .