The answer is the less dense plate slides over the denser plate.
What is that supposed to mean?
If the temperature is high there is less water because it evaporates if it is cloudy it is more because it doesn't evaporate
The gravitational force.
In fact, the motion of the projectile is composed by two independent motions:
- on the horizontal direction, it is a uniform motion (with constant speed)
- on the vertical direction, it is a uniformly accelerated motion, where the vertical acceleration g is given by the gravity exerted by the Earth on the projectile.
For this reason, the composition of the two motions results in a parabolic trajectory.