Ok, I know how to make my car bounce and move (I watched a youtube video), but how can I make it 1.accelerate by pushing up arrow key, 2.decelerate by not pushing any keys, and 3. make it decelerate with formula (base speed x sqrt of base speed) twice as fast by pushing down arrow? could someone post a project with the scripts and tell me so I can download it and figure out how to do this? I'll be sure to site you in my credits.

Where'd you get that base speed formula? It would be a lot easier to use this instead:

if <key [up arrow v] pressed?>
  change [velocity v] by (acceleration) //set 'acceleration' to any positive value
else
  if <key [down arrow v] pressed?>
    set [velocity v] to ((velocity) * (0.5))
  else
    set [velocity v] to ((velocity) * (0.95))
  end
end