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Name: Nathan U.
Status: Educator
Age: 50s
Location: N/A
Country: N/A
Date: January 2004


Question:
Our students claim that when a bullet emerges from a horizontal rifle, it can take a rising path due to the spinning of the bullet. Is there a way for a bullet to rise? We think that Bernoulli effect is minimal to null in this situation.



Replies:
Nathan -

A real bullet shaped projectile.... no. But a round projectile... maybe.

In aerodynamics there is an effect known as the Magnus Effect. It would likely not apply to a bullet because of its shape. The bullet would likely continue to fly with the nose forward and the rifling would turn the bullet around its longitudinal (front to rear) axis. However, the Magnus Effect could effect a round projectile as fired from a musket or an old fashioned cannon ball. This could cause the ball to rise if were rotated properly around its lateral (left to right) axis while in flight. (Think of hitting a cue ball with back spin on a pool table. That is the kind of spin it would need.)

I would expect that this effect would be most apparent with a slow-moving, light projectile of larger size. Perhaps it could be seen with slow motion photography if a Polystyrene foam ball were pitched with a great deal of back spin. I really do not know if it would be significant enough to measure, but it might be fun to try.

Larry Krengel


No way.

The fact that the bullet is spinning means that, on average, it's symmetrical about its line of flight, so why would any force exerted by air cause it to rise, rather than, say, go to the left? The only thing I can think of that would break the symmetry, and result in a preferred direction, would be *very* slightly higher air density below the bullet than above it, but this difference seems utterly negligible.

I don't believe a bullet fired horizontally actually rises, or even falls more slowly than it would if simply dropped. However, I do believe a rifle's recoil could cause it to rotate about its center of mass so that the barrel tips upward slightly while the bullet is still within the barrel.

Tim Mooney



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