#1
When you play over certain chords their are stong notes.

What happens in the case of power chords?
#2
power chords are peferct 5ths. its one of the main chords within another chord so it sorta depends on the mood you want to portray, I'm no theorist....
#3
If your rhythmn player is playing a C Major chord, then your strong notes are gonna be C, E, and G. You'll want to gravitate around those notes. If you play a scale that doesn't contain all of those notes, say C Minor, then it wouldn't work or sound good. But if your rhytmn player is just playing a C power chord, which is C and G, then it opens up a bunch more possibilities for the lead player. You could play in any scale or key that contains C and G and it would work. But the rhythmn playing would sound very bland if it's just a C power Chord.
#4
For melodic and harmonic purposes, I usually look at power chords as triads with the third taken out. For example, if we have the all too common progression that goes C5 G5 A5 F5, it's safe to assume that the song is in C, Am, or F (or Dm, but there is no Dm in the progression). This progression is most common in the key of C, as it is a I V vi IV progression, which is used in far too many songs. So, without any accidentals, these chords can be assumed to be (in "extended" form, for lack of a better word), C G Am F. This makes harmony and melody pretty cut and dry.

If you have a tonic-subdominant-dominant progression though, you'd have to look at context to tell whether it's major, minor, or harmonic minor. It's not as obvious whether it's I IV V, i iv v, or i iv V.
Only play what you hear. If you don’t hear anything, don’t play anything.
-Chick Corea
#5
Power chords usually imply the 3rd, so you can just work out if the third implied is a major or minor then treat it like a normal chord progression.
#6
Quote by 12345abcd3
Power chords usually imply the 3rd, so you can just work out if the third implied is a major or minor then treat it like a normal chord progression.

^they are implied usually. it would be like playing over just bass lines. even though the all the notes of the chord arent there, they are implied. but with just bass or power chords you have a little more freedom for passing tones because of the lack of other notes.
#7
Quote by 12345abcd3
Power chords usually imply the 3rd, so you can just work out if the third implied is a major or minor then treat it like a normal chord progression.


This.

C5 usually represents either C, Cm, Am7, or A♭maj7. With the seventh chords, the "root" and "fifth" are actually the third and seventh of the chord.