I live in Colorado, about 5,500' MSL. Today was hot and dry, about 95F. Density Altitude was above 9,000', maybe 9,200 or so. We watched a Piper Cherokee PA-28-140 takeoff with a mighty shallow climb angle, two on board. This led to me trying to explain Density Altitude to a non-pilot friend. He asked: How does this affect people? Is it just like being at higher altitude when climbing a mountain? Good question! I know there's less lift, and engines have less oxygen (but that matters less). But what about human performance? Is it the equivalent of hiking or being, in this case, at 9,200' MSL? I should know this, but I don't. What sayeth the gurus of POA? Thanks.