system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When swiping a card, you would think if you swipe slowly the machine could get a better read and accept your card. Why is this not the case? Why do you have to swipe it fast?
gpt
A magnetic stripe readers operates by listening to a magnetic field for changes created by the passing card.   A card moving faster creates what could be described as a "louder" "message".  

Ideally, a consistent, swift swipe produces the most clear "message" for the reader to pick up on, and it is also generally easier to maintain a more consistent card speed when the card is moving over the read head faster.