[Q] Does spin reduce resistance?

[paigetheoracle]

I've noticed that frisbees*, drills, javelins, propellers (planes, submarines, helicopters), arrows, rifling in gun barrels all cause spin or spin naturally. Is this because forward momentum creates displacement (pressure at the front/ vacuum at the back or in the case of deliberate propulsion as in jet engines, vacuum at the front, forward momentum from the back as the sucked in air expands at the back, pushing the craft forward)? (This is related to my thread 'Why do UFO's spin?' in the Weird claims forum).

 

Also does percussion as in hammer drills and the rocket that was supposed to be propelled by minor nuclear explosions (staccato versus smooth flow), have any advantage over spin (think also of nail versus screw or saw versus axe)?

 

*discs show lack of resistance all round, by transferring what part of the edge is facing forward as pointed objects keep the narrowest part of themselves in the forward position - likewise spheres spin in the same way as discs, being rotated by friction or is all of this conjecture aimed at trying to make sense of the phenomena way out because I'm not a physicist?

[stereologist]

The spinning adds stability to a bullet. It prevents the bullet from tumbling. A tumbling projectile is less accurate. This is quite evident if you try to throw a Frisbee without spinning it.

 

Arrows and spears do not usually spin. The fletchings on the arrow prevent spinning. Rockets do not spin. That would complicate guidance.

[paigetheoracle]

The spinning adds stability to a bullet. It prevents the bullet from tumbling. A tumbling projectile is less accurate. This is quite evident if you try to throw a Frisbee without spinning it.

 

Arrows and spears do not usually spin. The fletchings on the arrow prevent spinning. Rockets do not spin. That would complicate guidance.

 

I know rockets don't spin. I didn't know arrows were designed not to spin - what about bombs with fins, is it the same with them?

[stereologist]

I've thought about this for a while and I think that spin would increase resistance. This is off the cuff, but my reasoning is that the goal is have the smoothest flow of air over the surface of the object especially if the object moves quickly through the air. A spinning object would create additional disruption of smooth air flow. On the other hand a spinning object is more stable. A long thin object would be stable as well. It would tend to align itself with the direction of travel. Slight rotations would be met with forces that would realign the object.