A F5 (F Power Chord) chord contains the notes F, C. It is built from the formula 1 - 5, with F as the root.
What makes moving from E5 to F5 sound so tense?
They're one fret apart — the smallest move available on a guitar. Chords a half-step apart don't belong to the same key, so the movement refuses to resolve. That deliberate refusal is exactly what makes it sound cold and machine-like rather than musical in a traditional sense.