Talk:Impact depth

Accuracy of the approximation
Does anyone know how good an approximation this actually is? Or does anyone have a comparison of actual numbers for penetrators of various types into various materials at different speeds?

I suspect it's not great, considering how it doesnt take into account any aeordynamic/flow properties of the interaction. For example, running the numbers on a .50 cal bullet in air gives you (11.3g/cm^3) / (0.0012g/cm^3) * 5.75cm gives a maximum penetration (of air, so range) of about 500m. In reality, it's *lethal* range is over 3km, it's maximum range is quite a bit longer, subject to gravity.

Another possible source of error is the stipulation that the projectile be moving significantly faster than the speed of sound in the target material. This is unusual, with penetrators such as an APFSDS round moving at somewhat less than 2km/s while the speed of sound in steel is 6km/s. 70.70.240.116 (talk) 08:37, 12 July 2010 (UTC)

ridiculous statement about energy
"Such an impactor, at a speed of 59 to 159 km/s, carries less kinetic energy than an explosive warhead of the same mass carries explosive energy."

LOL. Removed.

59 to 159 km/s is extremely fast -- enough to escape from the solar system. Mass moving that fast carries much more kinetic energy than explosives of equal mass in chemical energy. (See Railgun and TNT.)

Even if thie sentence comes from the kinetic bombardment topic, it would be 5.9 to 15.9 km/s, the latter figures would still be somewhat exaggerated, and the statement about kinetic vs. explosive energy would still be false. - ¡Ouch! (hurt me / more pain) 15:20, 25 August 2011 (UTC)

energy and the intro
"Nothing is said about where the impactor's kinetic energy goes"

It is just heat. Does that even warrant mention? — Preceding unsigned comment added by 69.255.170.233 (talk) 20:03, 13 November 2012 (UTC)

Hmmm, in the end - yes. But in between Newtons idea (if I grasp it) is that kinetic energy is transfered to other masses - which for practical purposes means that even if the penetrator is stopped the debris may still kill people behind the (non-penetrated) wall (BASE - behind armor secondary effect). In my opinion the more interesting question would be how far any significant part of the original kinetic energy is projected in the direction of the original flight path. But that'S mixing theory and application - and there should be better uses for that approximation than just the obvious military one. --92.195.121.25 (talk) 05:51, 27 November 2012 (UTC)JB.

"high velocity?"
Article says:

"According to Newton's approximation, a uranium projectile at high speed and 1 m in length would punch its way through 6 m of rock (density 3 g/cm³) before coming to a stop."

When we're talking about "high velocity," are we talking about 100m/sec? 1km/sec? — Preceding unsigned comment added by 68.61.156.96 (talk) 21:45, 13 November 2012 (UTC)

Stopped in mid-air?

 * A smaller ice cube will be stopped in mid-air and explode. An ice cube with a diameter of 50 m or more, however, may also be stopped in mid-air, as long as it comes in at a very low angle and thus has to pierce through a lot of atmosphere.

How can it be "stopped in mid-air"? Surely it's still moving before it explodes!

Figure error?
If the equation only applies to blunt impactors, why is the impactor on the image pointy? 147.197.140.103 (talk) 17:13, 22 November 2012 (UTC)


 * It comes to a blunt point, rather than a sharp one.--MajorHazard (talk) 11:24, 11 July 2016 (UTC)

Regarding the accuracy of the approximation.
This approximation may be relatively accurate for target/projectile combinations of similar density (same order or magnitude, and provided the velocity is very high. It is true that a APFDS penetrator has a considerably lower velocity than the speed of sound in any of the materials involved in a typical impact. That is the main reason why, in order to create a good model of these type of impacts, several additional parameters must be added, such as the strength of each material etc... For impacts at significantly higher velocities (say >6000m/s) the simple equation becomes the dominant factor, e.g. the penetration of a steel plate by a HEAT jet. For impacts at lower velocities, there is a continuum in which this simple relation becomes less and less dominant. A low velocities its influence becomes non existent, as impacts where the projectile simply bounces off the target.  — Preceding unsigned comment added by Hmshare (talk • contribs) 11:03, 9 October 2013 (UTC)

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Misc.
Xkcd, anyone? — Preceding unsigned comment added by 70.77.81.186 (talk) 23:33, 7 April 2021 (UTC)