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Why do moving average acts as support and resistance?
As you point out, the moving average is just MA(k)t = (Pt-1 + … + Pt-k )/k and is applied in technical analysis (TA) to smooth out volatile (noise) price action. If it has any logic to it, you might want to think in terms of return series (Pt - Pt-1 / Pt-1) and you could hypothesize that prices are in fact predictable and will oscillate below and above a running moving average.  Below is a link to a study on MA trading rules, published in the Journal of Finance, with the conclusion of predictive power and abnormal returns from such strategies. As with any decision made upon historical arguments, one should be aware of structural changes and or data mining.  Simple  technical trading rules and the stochastic properties of stock  returns Brock, W., J. Lakonishok and B. Le Baron, 1992, Simple technical trading rules and the stochastic properties of stock returns, Journal of Finance, 47, 1731-64. MA rules betterthan chance in US stock market, 1897-1986 I don't know whether you are new to TA or not, but a great commercial site, with plenty of computer-generated signals is FinViz.