Landing the bottle whilst we waited

 We tried to land the bottle upright whilst we waited for the coach to be fixed.

 I'm no expert but my students pointed out from their experience that it depends on how full the bottle is.

 There are two bits of Physics going on. Whilst the bottle is spinning, the bottom of the bottle exerts a centripetal force onto the water to keep it moving in a circle and to stop it heading off in a straight line. The more the mass of water, the more the inertia so the bigger force needed to get it into a circle. The spinning bottle will then have more angular momentum. Momentum is a measure of how hard it is to stop something moving so with more water, the floor will have to exert a bigger force to stop the bottle.

The second bit of Physics is about stability. The bottle almost always lands on its edge at an angle. As long as the arrow showing its weight acting down through the centre of mass passes through the bottom of the bottle, the bottle will go back upright. The more water, the higher the centre of mass and the more likely the arrow is to pass outside the bottom of the bottle and tip the bottle.