I'm pretty sure it's the<span> impact of the air molecules on the outside of the stopper. They exert a net inward force, which is not resisted by anything on the other side.</span>
True. There are forced acting on it, but as they're balanced it is unmoving
<span>So we want to know how did the planets form in the Solar system. So the current most accepted explanation is accretion. First the Sun formed, and what has left was a disk made out of gas and dust which later formed the planets trough attractive gravitational force.</span>
