Maybe the apple is accelerated, since its velocity changes from zero as it is hanging on the tree and moves toward the ground.
That means that something acts on the apple to cause this acceleration. Let's call this "gravity",
I am gonna called net force
Something is acting on that horse that is causing the acceleration of that carriage...
I have another theory
The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
Hmm i want to do an experiment i had in mind a long time ago
What if a ball rolling down a hill will continue to roll unless friction or another force stops it.