system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: how does a computer trackpad or a phone screen tell if a finger is touching it or a brick?

Im asking because a finger will work, but no matter how hard you push with a brick nothing will happen.
gpt
Basically, behind the screen is a big grid of tiny capacitors. As our finger gets close to them, the electrical current changes due to the interaction with our body. Our charge reacts with their charge. The system is optimised to respond within the ranges that we produce.