Originally Posted by

**Gingervytes**
They ASSUMED incorrectly (on purpose), that there is an equal and opposite force from gas movement due to pressure gradient force. Escaping gas needs something to push off of

Mathematical proof that the thrust equation is false

Attachment 39978
Your proof appears to assume that the fluid in the pipe is never accelerated.

ETA: If you combine two equations and get a result that contradicts one of them, then you've made a mistake in your math. This is just a fact about math and says nothing about physics.