[clevernever (OP)]

The earth, the object and the plane (and the atmosphere) are all in the same system.

The earth interacts with everything (and everything interacts with the earth).

The object and plane only interact when they are touching.

Energy is conserved.

Mass is conserved.

Momentum is conserved.

Angular momentum is conserved.

Charge is conserved.

As long as the different models agree on these assumptions, it doesn't matter how we rationalize the interactions (rockets don't work because of the conservation of momentum any more than because of electromagnetism.)

So a person throwing a ball is equivalent of gas leaving a rocket due to pressure gradient?

[chiralSPO]

So a person throwing a ball is equivalent of gas leaving a rocket due to pressure gradient?

Insofar as momentum is conserved by splitting kinetic energy between masses that are accelerating away from each other in each case? yes!

[clevernever (OP)]

So a person throwing a ball is equivalent of gas leaving a rocket due to pressure gradient?

Insofar as momentum is conserved by splitting kinetic energy between masses that are accelerating away from each other in each case? yes!

So if a hot air balloon starts to lift off from the ground, does it push off the ground first?

[Colin2B]

So if a hot air balloon starts to lift off from the ground, does it push off the ground first?

No.
It’s a good question. Given what’s been said, think about it and see if you can work it out.

[Origin]

Deleted, question already answered.

[Colin2B]

Deleted, question already answered.

Didn’t see that, but it did appear there was sufficient info to work it out if not.