The conservation of momentum and Newton's 3rd law. If the wall moves, the ball slows down. Proof by counterexample
Joe Craine, the YouTube Martyr, created a video
http://youtube.com/watch?v=65Gvyv42Q2s
that directly proves
In a head on (depending on how you look at it, perpendicular) collision of a perfectly elastic ball with a perfectly elastic unmoveable wall, no momentum is transferred to the wall.
Another way of stating the same thing is
In a collision of a ball and an unmoving wall, if the ball bounces back with the same momentum (opposite direction) that it brought, the wall did not move in the collision and got no momentum from the collision.
Of course, no amount of proof will satisfy the NASA shills, so I had an ongoing discussion with NASA shill apollowasreal about the stench of a result in physics where a physical quantity (momentum) gets multiplied. That video
youtube.com/watch?v=65Gvyv42Q2s
proves it totally, but, apollowasreal would not accept a single CO2 molecule could not move an object held down by gravity, in the video I used the upper wall of the apollo 11 saturn combustion chamber.
I could not get apollowasreal to address the reality of the fact that, if the wall moved at all, the ball could not return with the same momentum (opposite direction). He fought the wall endlessly, but would not move into an area where I could use counterexample.
One of the important tools of disinformation is using name calling to try to reduce the trust of those reading the comments and the credibility of the person supporting the truth . A side effect of that name calling is sever arrogance. apollowasreal decided to correct his earlier mistakes about kinetic energy and "teach me a lesson" by pointing out that the wall that he contended would always move, got some kinetic energy in the transaction. Since the source of the kinetic energy was the ball, I had my counterexample.
apollowasreal needs the rocket exhaust molecules to impart momentum to the rocket, even though they are spit out of the rocket at tremendous speeds (creating pressure, by the way). To that end, the NASA contention is that the exhaust molecules impart twice the momentum they bring. This fails the smell test, but, as our nazi leaders have know for a long time, a big enough lie with enough difficult to understand information will make believers of the slaves.
The counterexample is fairly straightforward; if the wall moves at all, the ball moves away slower than it arrived. That violates the conditions. That proves the wall never moves and, thus, has no momentum.
QED
The law of the conservation of momentum is expressed as
When some bodies constituting an isolated system act upon one another, the total momentum of the system remains constant.
or
The total momentum of an isolated system of interacting bodies remains constant.
The mistake apollowasreal is making is believing that objects in the vicinity of each other, but not interacting, are considered when applying the law of the conservation of momentum. They are not. The law of the conservation of momentum only applies to objects that are interacting. The ball and the wall are not interacting until they collide at which point, the ball has stopped, equal to the wall. The total momentum of the isolated system is, thus, zero. apollowasreal insists that the momentum before interaction needs to be considered; it doesn't.
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