Penetration

http://home.comcast.net/%7Einfinitycrops/sperm.jpg

WARNING: THIS ARTICLE MAY CONTAIN SMALL TRACES OF SEMEN. Anyone with a receptive vagina should proceed with extreme caution.

see drill.

The act of thrusting the penis into the vagina.

Among other things.

The most easily remembered formula to calculate penetration is de Marre's

wv^2=kd^3(t/d)^n

(See tank)