Re: Why will i lean forward when my mom presses the brakes of our car?

You are noticing something physicists call conservation of momentum. The usual 
way of saying it goes back to Newton
Objects in motion (and you are the object) tend to stay in motion unless acted 
on by a force (the seat and seatbelt for you).

Your car is slowing down because of the brakes, and then you keep going forward 
at the same speed. Your bottom is sort of stuck to the seat, but your body leans 
forward until the seatbelt or your muscles pull it back.

Great question.
Keep noticing all the interesting stuff that makes up our natural world.

David Winsemius.