How Frictional Force Effects a Bullet While Spinning And Non-Spinning

You are right.

do the same principle apply when the fluid is water instead of air ?

do the spinning bullet undergoes less drag and friction ?

I think same principle will not apply when the fluid is water instead of air. Water has lot of resistance & hydrodynamics will decide.

am i wrong if i take the following line as reference..

a screw needs less force than hammering a Nail into a solid block !

if not a screw, even in case of nail it will easily penetrate into a semi-solid while twisting...

but i'm still in a dilemma how spin will work regarding forces under water.

could you please clarify it to me sir...

Within a very short time, the spin should stop due to the resistance of water.

i can't give you a diffinative answer. rotational spin only stabilizes the bullet.. in theory,, one benitifit of the inertia energy that is used to stabilize the bullet would detract from propelled speed.

i'm wrong. the energy needed to rotate the bullet was spent in rifle barrel.

wen the bullet leaves the barrel it has energy in two forms: as kinetic energy due to its velocity in axial direction ans a second enrgy due to the rotation imposed during its travel in the barrel. The first is mv²/2 and the second is Jω²/2. In its movement in the air 2 friction occur since the combination axial + rotational movement leads to a complex air (or fluid ) pattern around the bullet. You can NOT compare with friction between solid bodies separated by a thin lubricant layer. It is totally DIFFERENT. As it was already mentioned spin is induced only to stabilize via a gyroscopic effect the bullet on its path. This has a positive aspect with respect to drag reduction because the bullet presents the smallest area to the air and it is known that drag force is proportional to frontal area.