How do you make self propelled toys?

How do you make self propelled toys?
for something to move it needs force . force can be energy.force equals mass and acellaration.basically,mass needs force to move. if you want to make a self propelled toy , you either need to make a chassis or frame for the toy.then you need to add wheels because for it to be self propelled,it needs to be on an inclined plane.that way gravity can pull it down.if you want it to be a flying self propelled plane it needs to be on a very large slope,it needs to have a frame ,a body,a propeller or two,large wings,and the slope needs to have a ramp.for it to be a car it needs wheels,a chassis,and a body.it needs to be on a slope without a ramp.for a self propelled boat,you need a frame,something heavy to create momentum like a metal wheel inside one of the toys that you push and they keep on going.you need some thing to catch the waves and make the metal wheel spin.then you need something like the things on the back of old steamboats.good luck!