But it can't move because of the presence of this barrier, the hydrophobic core. So what we have happening is we have another force that points in the opposite direction, the force due to the presence of this hydrophobic barrier. Let's call that simply FH. And so these two forces point an equal and opposite direction. So they're equal in magnitude, they point in opposite directions. And so this marker is not going to move in the same way that the sodium ion is not going to move because of the presence of the hydrophobic barrier.