Sectional density

Sectional density (often abbreviated SD) is the <a href="/facts/Ratio/mFmhQt7T">ratio</a> of an object's <a href="/facts/Mass/HHdc8XmF">mass</a> to its <a href="/facts/Cross_section_(geometry)/g5R1c6v2">cross sectional</a> <a href="/facts/Area/KsNG1G9t">area</a> with respect to a given axis. It conveys how well an object's mass is distributed (by its shape) to overcome resistance along that axis.
Sectional density is used in <a href="/facts/Ballistics/3WHTox0u">gun ballistics</a>. In this context, it is the ratio of a <a href="/facts/Projectile/kaDpG3N7">projectile</a>'s weight (often in either <a href="/facts/Kilogram/lU2zbPk8">kilograms</a>, <a href="/facts/Gram/CNAPqWKz">grams</a>, <a href="/facts/Pound_(mass)/BNIGRRDI">pounds</a> or <a href="/facts/Grain_(unit)/kkDKk6na">grains</a>) to its <a href="/facts/Transverse_section/L4STR2tR">transverse section</a> (often in either <a href="/facts/Square_centimeter/u5nT9y0W">square centimeters</a>, <a href="/facts/Square_millimeter/u5nT9y0W">square millimeters</a> or <a href="/facts/Square_inch/HMKj3Jok">square inches</a>), with respect to the axis of motion. It conveys how well an object's mass is distributed (by its shape) to overcome resistance along that axis. For illustration, a nail can penetrate a target medium with its pointed end first with less force than a coin of the same mass lying flat on the target medium.
During <a href="/facts/World_War_II/2efV5L1U">World War II</a>, <a href="/facts/Bunker_buster/HmzyvGPs">bunker-busting</a> <a href="/facts/R%25C3%25B6chling_shell/lUE7md5j">Röchling shells</a> were developed by German engineer <a href="/facts/August_Coenders/Itot92M1">August Coenders</a>, based on the theory of increasing sectional density to improve penetration. Röchling shells were tested in 1942 and 1943 against the Belgian <a href="/facts/Fort_d%2527Aubin-Neufch%25C3%25A2teau/j03PDTsW">Fort d'Aubin-Neufchâteau</a> and saw very limited use during World War II.

Sectional density open-in-new

Sectional density