Simple proof, rockets don’t work in space vacuum: get a pipe with only one side open. Put closed face down on a scale. Remove the air from the pipe with vacuum. Where is the opposite force on the scale? I didn’t see it.

Now lets say you put an object, let say a few pennies that weight approx 3 grams each. Now the airflow is strong enough to lift those pennies against gravity. Shouldn’t I see a force greater than the normal force of the pennies?

Source from nasa states that the force it takes for the mass to move out from the rocket, is applied equally and oppositely on the rocket. Now the pipe experiment disproves this as there is no evidence of opposite force onto scale when air or even objects in the pipe move out.

Additionally, Joules expansion shows that no work is done when gas expands into a vacuum. Furthermore, thermodynamics states. Work=-external pressure *change in volume. If external pressure of space is 0, work done is 0.

Furthermore, NASA tends to concentrate on velocity rather than flow rate. Use of a nozzle. A smaller diameter pipe, increases the velocity, but leaves the flow rate unchanged. Flow rate is dependent on pressure differential. [link to www.1728.org]

If velocity (meters per second) is of importance rather than flow (kilograms/second), it makes more sense that the gas pushes off the atmosphere. Similarly, a car going at faster speed would generally have more drag.

Just like energy is required to move objects to a higher height (gravitational potential), energy is required to create pressure (energy from combustion). Therefore gravity and pressure are both potential energies.

To sum it all up, when you drop an object from a height, there is no opposite reaction on your hand because gravity causes a force (Force=mass*acceleration). Similarly, pressure gradient also causes a force [link to en.m.wikipedia.org (secure)]