system
Given the following post, respond as if you're commenting on Reddit:
human
[Any] There’s a common thing of energy shields blocking projectiles, but not people, how does it distinguish the difference?

This is mostly referring to video games, and it could be its for gameplay reasons in a lot of them.

Like, let’s say the Bubble Shield form the Halo series. People can walk in and out just fine, but it’s able to stop bullets. How? 

If it somehow just detects that kind of projectile, wouldn’t it just not allow the whole gun, that has bullets in it, through the threshold?

Thanks in advance!
gpt
The Codex in Mass Effect actually brings this up. In short, the shield uses mass effect fields to manipulate an area of ozone around the shield's wearer with a VI (a computer) running scans and calculations to see where it needs to enhance the shield to block incoming attacks.

But one of the things that it takes into account is the velocity of a projectile; if it's going too fast, it's automatically flagged as something that needs to be blocked. But if it's too slow or stationary then the shield won't react to it.

This means that if you go to sit down in a chair, the shield won't react and push it away.