I made this observation but could not find any research to vindicate my hypothesis. Perhaps nobody has given it a thought. When you think of Arnold Schwarzenegger in Terminator 2 – the first scene you recall might be a one in slow motion. On the other hand when you think of Charlie Chaplin or a similar funny character – you might remember a fast forward scene. Why do humans use slow motion to emphasize strength and seriousness, and fast forward for something funny and trivial?
Evolution might have the answer. Big animals move slowly. Elephants, rhinos, hippos, and lions. Even when they move fast you see the motion of their legs, and their motion on ground relative to their size. This relative perception registers their motion as “slow(er)”. This slow perception triggers respect, seriousness, fear and all those emotions these animals have gained over millions of years of evolution.
Now think of insects. Ever seen a cockroach scurry around? You think it is fast, don’t you? It is because you see not only its motion relative to its size but also the motion of its legs relative to one another (fast changing angles and rapidly closing gaps). You perceive these motions as non-serious and funny because you, I mean the primitive you, generally won’t fear for your life when you see an insect. I wonder if cockroaches knew this and moved in slow motion.
Another related question – why humans find shades impressive – dilated black pupils as sign of good health perhaps? Now think of a cockroach wearing shades and moving in slow motion. Impressive isn't it?