the forces of elastic, gravity and more
You can put a rubber band on 2 sticks then you put it (the rubber band) around the cart then pull back then you let it go to slingshot it across the floor. A way to make it twice as powerful ( the rubber bands elastic force) is to double up the ruber band then reapeat the stuff before.
The difference between mass and weight! well mass affects wieght because gravity affects mass makeing wieght