How come asteroids don’t falls straight down, due to Earth’s gravity? They should be pulled through space straight towards Earth for millions of miles, right? But I see videos of them streaking across the sky horizontally.
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They are pulled towards Earth, but that doesn’t mean they’re *moving* straight down. The pull is acceleration (*change* in velocity), the second is velocity itself. For a more elementary example: imagine you’re running forward, attached to a long elastic band. You can still be moving forward (forward velocity) even once the band begins to slow you down (backward acceleration). Or imagine rolling a ball across a sloped surface: gravity always pulls downward, but the ball follows a curved trajectory on the surface that depends on how it was rolled.
An meteor ( comes in moving very, *very* fast. So their velocities aren’t usually straight down. They actually will usually be somewhat close to straight-down – they’re not moving as horizontally as it looks like they are – but there’s no perspective for you to tell the up-and-down part of their motion from so far away. So you just see the side-to-side part, which is usually not zero. To see this in action with a *lot* of meteors, you can look at [a meteor shower](https://en.wikipedia.org/wiki/Radiant_(meteor_shower)#/media/File:Geminid%C3%A1k_meteorraj_maximuma_2007-ben.jpg), which will appear to “radiate” from a single point in the sky. What you’re seeing there is the direction the meteors are coming in from, and the random side-to-side motions around that direction carried by each individual meteor.
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