Recent near misses by asteroids, when you think clearly about them, clearly present two dangers:

1. the object is large enough and slow enough to be influenced by gravity and survive the atmosphere

or

2. the object is moving so fast, the opportunity to change its path using gravity is very short lived.

Fortunately the ones in the second category are usually too small to survive the atmosphere.

Cat 2: very fast, tree house size, VERY close (14,000 kms, about the diameter of the Earth, so you could say it missed us by one day, though it would not be accurate). 3rd closest non-impacting asteriod on record.. More about this event.

2009 VA mag=12.2 Nov 06 21:00, dist=0.000136 A.U. Nov 06 21:36, speed=4392.12 arcseconds/min Nov 06 21:00, diam=5-11 m

Cat 2: fast, truck size, about 1/2 distance to moon

2009 WJ6 mag=15.3 Nov 20 09:00, dist=0.001187 A.U. Nov 20 09:36, speed=1284.9 arcseconds/min Nov 20 11:00, diam=8-19 m

Cat 1: slow, city block size, over 6 million miles away

2000 XK44 mag=13.4 Nov 05 03:00, dist=0.07395 A.U. Nov 04 09:36, speed=8.45 arcseconds/min Nov 04 18:00, diam=637-1425 m