Elastic Force & Gravity
One way you could propel a cart across the floor is to pull it with a rubber band. But that is boring and plain and unoriginal. Another way to move the cart is to snap the rubber band on the back of the cart so the cart propels forward. You could also twist the rubber band around so the wheel flies forward. You could also make a catapult.
But enough about that, now is a time to talk about the difference of mass and weight. Mass is more like how much space you take up. As weight is how much gravity is pulling you toward the center of the earth. To measure mass you use a balance. To measure weight you use a scale. We learned how the increase of mass increases the weight. We measure mass in grams and kilograms. We measure weight in pounds or newtons.
Force is a push or pull. Force affects something or causes something to happen.