Astrophysics peeps, why is it that the danger seems to be only tied to the mass of the object. Given p=mv is (relative) speed essentially the same for all of them or otherwise inconsequential?
The range of mass is typically much larger than the range of velocities. There is an upper bound to the speed for the vast majority of things which are dangerous (escape velocity of the solar system). However there are orders of magnitude differences in mass.
Adding a little context for those not familiar with orbital mechanics: the speed of a circular orbit is directly related to its distance from the barycenter (i.e. the Sun). The asteroid belt is between the orbits of Mars (orbiting at 24km/s) and Jupiter (13km/s). Whilst an asteroid that strays far enough to hit Earth (orbiting at 30km/s) is by definition not in an exactly circular orbit, nor one always between Mars and Jupiter, the difference in speeds isn't that great. That accounts for ddahlen's point about the limited range of velocities.
A very rough calculation of mine involving a hypothetical asteroid in a elliptical orbit extending as far as Jupiter and right down to Earth, assuming no difference in orbital inclination to Earth and no significant gravitational perturbations, would result in a relative speed of 5km/s. The actual impact speed would be greater due to Earth's own gravity, adding an extra 11km/s.
Not all asteroids are from the asteroid belt, but I am under the impression that visitors from the outer solar system (which could be as fast as the upper bound that ddahlen mentions) are much more infrequent than stray asteroid belt objects, so the median impact speed would still be relatively slow.
Earth's orbital diameter is: ~30 x 10^7 km
number of seconds in a year is: ~ π x 10^7 s
so, Earth's orbital velocity is: ~30 km/s
speed of light, c, is: ~30 x 10^4 km/s
so, Earth's orbital diameter is: ~ 1,000 light seconds
and, Earth's orbital velocity is: ~ 0.0001 c
We have spotted a grand total of 2 interstellar objects, they were moving faster, but are many orders of magnitude less numerous then the local stuff.
Just doing some back of the envelope calculations, looks like Omuamua was moving about 165,000km/hr (relative to Earth) when it was about at Earths orbital distance.
This speed is not actually a crazy number, it is a lot faster than the majority of things which could hit us, but there are geometries of things in our solar system which can reach these relative velocities. (For example things in retrograde, IE: reverse orbits) can lead to basically escape velocity + earths velocity.
I'm not an astrophysicist, but I was part of a D&D group with one a few years ago and the topic came up (outside the game). In practice the speeds fall into two fairly tight clusters (asteroids and comets), but you don't even need that to justify focusing on mass. There's a hard lower bound on everything, and also a hard upper bound on any object that is part of our solar system, and it works out to at most a factor of 40ish in kinetic energy between the slowest and fastest possible impacts. The masses of objects of interest have a much wider range.
Everything coming in speeds up when it falls to earth.
Tiny stuff burns up completely in the upper atmosphere, where the pressure is low, because they have low surface area per mass -- the atmosphere can stop them entirely. Their terminal velocity is low. (That is, when the velocity through air is high enough that the drag prevents gravity from speeding up the object any further.)
Medium objects have a higher terminal velocity get deeper into the atmosphere before exploding. Fragments from these (which now have higher surface area per mass) can then be slowed further by the atmosphere and make it to the surface, but not so dramatically. Bits of the Chelyabinsk impactor fall into this category.
Big objects have a high terminal velocity. They make it to the ground largely intact... and without being slowed as much by the atmosphere. That gives you craters and bad days for being a dinosaur.
Not into astrophysics, but I guess "faster asteroids experience higher forces when going through the atmosphere, therefore burning faster". Another explanation could be "most of asteroid's speed comes from Earth's gravity, not from it's initial state".
These are just random guesses though, so I could be completely wrong.
