General physics I get. Bike physics though...

Anyway, I ask because I just built the bike, brand new chain, and I know chains stretch over time. When I started, the chain tension was pretty tight, but I think it loosened pretty quickly. The other day I was riding home and I went to start pedaling after stopping to drink, and it felt like the chain skipped and caught or binded, not sure I didn't see it, just felt the shudder. Just checking the tension it was much more loose.
The brief moment I was referring to before the chain "engages" was you when you're coasting and you go to pedal again, there might be this split second where there seems to be no resistance before it kicks in and you know you're putting effot into it. I'm guessing that's maybe some slack? I dunno.

maybe i'm crazy.