At 5:51 PM 2/16/5, Robin van Spaandonk wrote: >In reply to thomas malloy's message of Tue, 15 Feb 2005 22:56:48 -0600: >Hi, >[snip] >>>If a smaller and a larger sphere collided at just the right speed, >>>you might get a ridge line where they joined, and the resultant >>>object would not be spherical because the two spheres were different >>>sizes. However it would have to be a fairly slow collision, >>>otherwise the energy of collision would melt both bodies, and they >>>would solidify as a perfect sphere. >> >>Isn't a slow collision between two astronomical bodies oxymoronic? > >Not necessarily, if they are moving together in the same direction, then >the differential speed can be very small (otherwise it would be impossible >to dock with the ISS).
The velocity of collision of two bodies of mass and radius M, R, m and r respectivley, is gravitationally bounded (on the low side) by V = (2 G M/(R+r))^0.5 + (2 G m/(R+r))^0.5. In the case of a body docking with the space station both M and m are very small. In the case of planet or moon sized collisions, M and m are large, so the total kinetic energy is large and thus V is large. Regards, Horace Heffner
