Time stops everything is made out of atoms so if atoms freeze everything freezes
Using the phase diagram of methane, the pressure and temperature play a critical role in its stability since a slight change in the pressure or temperature will cause a phase change. At low temperature and high pressure, methane hydrate becomes solid (methane hydrate + ice). When the temperature is increased, it becomes liquid. This is one of the main challenges in harvesting methane hydrate, its instability.
I expect that they will <em>add</em>, and their effect at every location will be the <em>sum</em> of their individual effects at that location.
For example:
If they're acting at the same point and in opposite directions, the effect will be the same as a single force at that point, with strength equal to their difference, and in the direction corresponding to whichever one is stronger.