Technical answers for Velikovsky fanstasy

Rotating objects have momentum, called angular momentum. For the Earth, that amounts to about 5.9 x 1033 kg-m2/sec. Now imagine an asteroid hitting the earth a grazing blow right on the equator. That would be the most effective way an asteroid could change the earth's rotation, either speeding it up or slowing it down. The asteroid has angular momentum relative to the center of the earth, equal to its mass times its velocity times the distance to the center of the earth. Typical impacts in the inner solar system involve velocities of about 30 kilometers per second, and for a grazing impact the distance from the center of the earth will be 6400 kilometers. In meters, those figures are 30,000 and 6,400,000, respectively. So to have angular momentum comparable to earth's we have mass x 30,000 x 6,400,000 = 5.9 x 1033, or mass = 3 x 1022 kilograms. Since the earth itself has a mass of 6 x 1024 kilograms, we're talking about something with 5 per cent of the mass of the earth, or about 4.5 times the mass of the moon. This is way bigger than any known asteroid.How would this affect the earth? The asteroid has kinetic energy = 1/2(mass)(velocity)2. = 1.3 x 1031 joules. Let's assume the asteroid stops the earth's rotation cold. That means that 2.1 x 1029 joules of its energy goes into stopping the earth's rotation, leaving about 98 per cent expressed in other forms, like heat. It takes 400,000 joules to melt a kilogram of rock, so there's enough energy left over to melt 3 x 1025 kilograms of rock. That's about five times the mass of the earth. Even allowing for a lot of energy radiating to space or being blasted off as ejecta, this puppy will melt most if not all of the earth. So don't sweat the long-term environmental effects. If the earth is ever hit hard enough to affect its rotation, nobody will be around to tell about it.On the other hand, an asteroid 10 kilometers in diameter, comparable to the one that caused the extinction of the dinosaurs, would have a mass of 1.5 x 1015 kilograms. If it hit the earth a grazing blow on the equator, its angular momentum would be 1.5 x 1015 x 30,000 x 6,400,000 = 3 x 1026 kg-m2/sec. That's about 1/20,000,000 of the earth's angular momentum, meaning it could change the earth's rotation by about 1/20,000,000, or change the length of the day by about .004 seconds. This is pretty tiny, but still several thousand times the effect of the great 2004 Indonesian earthquake. Even an impact big enough to cause a global catastrophe would still have only a tiny effect on the earth's rotation.