I got an idea for a nice game, but i need a velocity and gravity script. I searched a lot, but i didnt find anything good. Let me explain: a ball will roll down a small hill and will gain speed at the same time.
http://scratch.mit.edu/projects/25446100/ <— easier explanation.
PS: i need that the ball will roll smooth and wont just randomly stop.
Thanks.

I can't really help too much with gravity, but I'll show you a velocity script:

when green flag clicked
set [xvel v] to [0]
forever
if <key [left arrow v] pressed?> then
    
change [xvel v] by (-1)
end
if <key [right arrow v] pressed?> then
    
change [xvel v] by (1)
end
set [xvel v] to ((xvel) * (0.9))
change x by (xvel)

Well, thanks, now i need only a gravity script.

define apply_gravity
    set [yvel v] to (0)
    reset timer
    repeat until <touching ground>
        change [yvel v] by ((timer)*(-9.81))
        // assuming a pixel is a meter. If you have a bigger unit add more multiplication here
        // also, the acceleration is -9.81 instead of 9.81 because down is negative y
        // 9.81 is the acceleration of earth's gravity near the surface
        change y by ((yvel)*(timer))
        // this isn't the most accurate thing ever because it discretely calculates velocity and position
        // you'll need calculus for more accuracy
        // but I'm assuming this is good enough
        reset timer
        // the timer makes sure this runs mostly the same with or without turbo mode and on different computers

HTH

$(".box-head")[0].textContent = "committing AT crimes since $whenever"

I will give it a try and say what happened.