Momentum in Physics is a fact proven a million times over - in other words it is an objective standard of measure. Rsi is invented by wilder. I personally prefer to follow the objective laws of physics rather that some random idea.
But nothing to stop you using both if that's your cup of tea.
Momentum in physics is about the movement of physical bodies. Why should that have any relevance to something non-physical like the price of shares other than as a descriptive analogy?