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Bullet Drop Brain Teaser

By Jeff Johnston

Before it became unpopular to talk about guns in school, physics teachers would often use this bullet-drop brain teaser. Do you know the answer?

The Myth
If a bullet is dropped from the bore of a rifle while another bullet is simultaneously shot from a bore of the same horizontal-to-the-earth rifle, both bullets will impact the ground at the same time.

The Expert Explanation
(courtesy of the NRA Firearms Fact Book)
If you are in to this stuff, you must have a Fact Book. NRA has been sold out for years, so buy one from Amazon.

“This would be quite true if the experiment took place in the airless environment of outer space. On the surface of the earth, where most of us do our shooting, however, the additional force of air drag must be taken into account. If air drag were directed only horizontally, it would make no difference to the speed with which the bullet falls. But because of the downward curve of he bullet’s flight, and the fact hat its point usually does not lie exactly in the direction of its flight, the drag has a slight upward component that resists the bullet’s fall."

The Conclusion
The horizontally fired bullet in a resisting medium like air takes a little longer to reach the ground than a slug dropped from the muzzle.

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3 Responses to Bullet Drop Brain Teaser

Tom P wrote:
May 27, 2011

That scenario is meant only to show the simple fact to high school freshman in science class about the acceleration due to gravity. They don't need to know yet about drag coefficients, lift, and curvatur of the earth. Just let them get the basics then worry about the details.

Dr. BS wrote:
May 19, 2011

Mr. Armstrong, Sounds to me like you're calling 1-800-Bullshooters! That's the spirit! While I am not a real Dr. of physics, I play one on this blog. However, my sources, Mr. Julian S. Hatcher and William C. Davis are the Albert Einsteins of ballistics. The NRA Fact Book, which I cited, is their accumulated knowledge via mathematics, Issac Newton's Mathematical Principles of Natural Science and actual testing at Aberdeen Proving Grounds. You will be hard pressed to argue the fact concerning Time of Fall that I quoted, unless, of course, you are from Mars or another planet unaffected by gravity. Thanks for reading! --BS

Allan Armstrong wrote:
May 19, 2011

Just another example of junk science. Where's the data, what are his sources?, flight extended by exactly how much, under what conditions? If this is the best he can do get him off the pages.