Ok, so I'm a bit confused by the derivation of a=v^2/r in Feynman's "Six Not-So-Easy Pieces". In pages 17-18, it is stated that "The other component of acceleration, at right angles to the curve, is easy to calculate, using Figures 1-7 and 1-8. In the short time Δt let the change in angle between v1 and v2 be the small angle Δθ. If the magnitude of the velocity is called v, then of course Δv ┴ = vΔθ and the acceleration a will be a┴ = v(Δθ/Δt).". 1) What velocity does he refer to by v? 2) How can he multiply Δθ (an angle) by v (a magnitude of a velocity)? 3) (Probably the same as 2) How can he divide Δθ by Δt? I haven't read the rest of the book, so maybe that's where the answer is? I don't know, it seems very weird.