I know that we cannot feel velocity we feel acceleration in a car. But why tho?
In: Physics
The theories that made Einstein famous (Special and General Relativity) both deal with the fact that there is no experiment you can do to determine if you are being accelerated or you are in a gravitational field; they are exactly identical in all scenarios. [PBS Space Time](https://www.youtube.com/c/pbsspacetime/videos) on youtube did a good series of videos about this recently, but to *way* oversimplify, the universe doesn’t care if you’re on an accelerating rocket in space or on the surface of a planet; the results of any experiment are always the same.
As for why we feel acceleration but not velocity, imagine this scenario: You and I are both astronauts in space, and there is nothing else around us to measure our position by. The distance between us is shrinking. Who’s moving? Are you coming towards me while I’m still, is it the other way around, or are we both moving towards a common center point? Answer: it doesn’t matter. Physics literally does not care which of us is “doing” the moving, and any of those three possibilities are all equally and simultaneously true.
Because you can’t really say who’s doing the moving, you can’t ever build a machine or grow an organ that can detect absolute movement, because as far as it’s concerned the entire universe might be moving around it while it’s stationary. Thus, you can’t feel constant velocity.
You can, however, feel forces quite easily, since applied forces and momentum work together to cause objects to bend or lag behind (imagine moving only one end of a spring and watching what happens to the other). Since acceleration is nothing but the result of a force applied over a period of time, you can quite easily measure acceleration too. But to circle back around, you can’t ever tell if that acceleration was due to gravity or it was due to an outside force.
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