metal jet from the cone shaped metal lining). This jet may then be viewed as the impactor of Newton's approximation. Meteorite: As may be concluded from the air pressure, the atmosphere's material is equivalent to about 10 m of water. Since ice has about the same density as water, an ice cube from space travelling at 15 km/s or so must have a length of 10 m to reach the surface of the earth at high speed. A smaller ice cube will be slowed to terminal velocity. A larger ice cube may also be slowed, however, as long as it comes in at a very low angle and thus has to pierce through a lot of atmosphere. An iron meteorite with a length of 1.3 m would punch through the atmosphere; a smaller one would be slowed by the air and fall at terminal velocity to the ground. Impactor, bunker buster: Solid impactors can be used instead of nuclear warheads to penetrate bunkers deep underground. According to Newton's approximation, a uranium projectile (density 19 g/cm3) 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. See also Impact force Further reading External links Earth Impact Effects Program Space debris penetration depth by velocity and diameter Projectiles Isaac Newton