# How fast would an object have to move to create a vacuum behind it?

When an object moves, I assume that the air above it, instead of remaining at the same general height, is pulled downward as it is passed in order to fill the low-pressure area behind the object where air was just left behind.

So if that's correct so far:

Assume we have a cube (1 m x 1 m for example) that can move very fast at perpendicular angles to it's sides (up, down, left, right, front, back).

At sea level, how fast would the cube need to move to reach the point where the force of displacement is higher than the force of the low-pressure zone attracting the air passing over the cube, causing a vacuum to occur?

Or rather, is there no speed at which this vacuum would be created?

• Define what you mean by 'vacuum'. It's not possible to have a perfect vacuum - even deep intergalactic space has some level of partial vacuum. – Time4Tea Jan 22 '15 at 21:37
• Relevant / interesting / related: what-if.xkcd.com/1 – Brandon Enright Jan 22 '15 at 21:57