| If the foam ball you drop is large enough losses from ablation wouldn't be a big deal. You can certainly get the speed down enough so that the words impact crater wouldn't be in the report, also you smack them into oceans not land (though smacking them into the desert would be an option I guess if you could shed enough speed). For a 10 meter sphere of nickel foam with a density of 2000kg/m3 (so about 60% 'air' by volume) it's ~2000 miles per hour[1]. http://hyperphysics.phy-astr.gsu.edu/hbase/airfri2.html#c5 Fast but not insurmountable. That sphere would be ~8000 tonnes of pure nickel minus ablative losses (which would reduce the impact speed). Of course you'd want the density to be below 1000KG/m3 or it'd sink. So a 10m sphere at 850kg/m3 would have a terminal velocity of ~1300 miles per hour - or about mach 2 and you'd be picking up about 3500 tonnes of pure nickel bobbing about. I'd quite like to see that actually (from a good distance away). |
Not a physicist, but my thinking would lead me to say that when this ball hits the water (after having already been heated a bit by ablation on the way down) it is going to compress into a pancake. Assuming the energy released at impact does not break the ball into lots of smaller pieces, the energy of the impact is going to vaporize a lot of water and melt a lot of nickle. I think what you are going to end up with after the large impact event is a compressed blob of nickle that is now rapidly sinking to the floor of the ocean.
We already know what happens to big chunks of metal from outer space that impact the surface of the earth, it tends not to be pretty. Oh yeah, and try to convince any country on the planet to let you drop your giant ball of awe-inspiring kinetic energy on a path that happens to cross over them. Not. Going. To. Happen.