REPORT ABUSIVE REPLY
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Message Subject
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NASA Thrust Equation gets destroyed.
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Poster Handle
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Anonymous Coward |
Post Content
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Not again that idiot who doesn't know what to substitute and doesn't know how to get units out of an equation (in a previous video he was including pi and constants in the units results which is totally wrong when you try to get units out of an equation). BTW "NASA thrust equation" isn't NASA's to begin with...
The definition of force is that it is equal to the change in momentum thus
F=dP/dt where P=m*u (mass times velosity)
and since we have change in mass and in speed we use the differentiation product rule, thus
F=dP/dt=d(m*u)/dt=u*dm/dt+m*du/dt
the thrust is the part of the force created by the rate of change of the mass
Ft=u*dm/dt
Even when substituting as per the video, the final units are as expected Kg*m/sec^2. That guy obviously is using some equation tables without actually grasping the real meaning of these (he for example used equations for a cylindrical pipe, not a more generic equation like A for area with units m^2 or V for volume with units m^3, another sign that he is not that of a knowledgeable person). He ignores conservation of momentum in a system and he is using a flawed example to prove nothing but his ignorance.
Quoting: Anonymous Coward 37509171 Would you point out the exact error? The equation is on NASA website So they promote it. I didn’t say anything about the units. The units are fine. There’s nothing wrong with the substitution. The velocity in the nozzle pipe is equal to the exit velocity. It’s simple. The conservation of momentum is conserved because the external force is pressure gradient force, not because the rocket pushes it.
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