Newton's Third Law of Motion

For every action there is an equal opposite reaction.

Note that the action force and the reactant force are acting on different objects.

This is why the $F_N \neq \text{ the reactant force of weight:}$as its instead

The gas is accelerated downwards through explositions and combustions.

Every object is like an elastic band, although not as readily elastic.

Although self explanatory, an object is only able to be put in motion by a force that was exerted on the object. A force exerted by an object does not influence that object.

Therefore, the prepositions on and by are very important and should be used with care.