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Name: Cameron
Status: student
Grade: 9-12
Country: USA
Date: Fall 2013


Question:
How fast would a bullet need to travel before the friction of the air would melt the lead core?



Replies:
That is not the major issue, the major factor is military projectiles are not simply lead. They are often uranium!! When uranium encounters the deceleration of a “hit” the temperature rises above the auto-ignition of uranium. This “burning” projectile melts through the armor of the target – whether steel or concrete – and “burns its way through the armor into the inside of the target, where it undergoes exothermic oxidation igniting any combustible material (such as humans) inside the armored vehicle, plane, or ship. Technology is great, but War is Hell.

Vince Calder


Hi Cameron,

Thanks for the question. I will not solve the problem exactly for you as I think it is good for you to try it on your own. You should set the kinetic energy equal to the energy needed to raise the temperature of the lead from room temperature to its melting point and the energy needed to melt the lead. You will find that the final answer does not depend on the mass of the bullet. From the expression above, you can solve for the speed, v. You will need to look up some information such as the heat capacity of lead, the melting point of lead, and the heat of fusion for lead.

I hope this helps. Thanks Jeff Grell


That is a very good question, Cameron, and there is no easy answer. First of all it would depend upon the type of gun the bullet was used in, and the type of bullet, the initial temperature of the bullet, as well as the mass of the explosive charge. That is because the bullet would gain significant heat before it ever left the barrel of the gun. The explosion of the propellant would heat it, and so would the friction of the barrel as the bullet spun its way through the rifling and out of the barrel. Then there might be additional heating or cooling depending upon the temperature of the air and the velocity of the bullet, and how long it was in the air. The friction of the air against the bullet as it traveled would be based upon the diameter and shape of the bullet. Once the bullet struck an object, most of it's momentum would be transformed into heat energy, especially if the bullet hit something really solid, that didn't offer much "give" when hit.

I am not an expert on bullets, but I would not expect that bullets melt very often.

Hope this helps. Jerry Gardner



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