Video narration
Why does a shopping cart keep rolling after you let go? That's inertia: with zero net force, its motion stays the same; it needs no continuing push. Friction acts against the cart's motion, changing it. Push harder, and it speeds up more; load it more, and the same push speeds it up less. Your hands push the cart; it pushes back on your hands: action-reaction, on different things. It keeps rolling until friction slows it.