The ball has to push things out of its way in order to keep going.
For example:
-- billions of air molecules
-- hundreds of blades of grass .
-- To push something out of its way, the ball exerts a force against the
obstacle, and pushes it some distance.
-- A force acting through a distance is 'work', and that means 'energy'.
-- The ball has a certain amount of energy ... the amount you gave it
when you kicked it. It gives every air molecule and blade of grass a
little bit of energy, so the ball has less and less as it goes along.
-- Eventually, it has no more energy to use to push things out of the way.
No energy means no motion, so it stops.
-- If it were in space where there are no air molecules and no grass,
it would go on forever.
