Yes, these are completely normal actions for the penis and scrotum. The balls, particularly, are constantly being adjusted toward or away from the body in order to control temperature. They like to be about 4 degrees cooler than body temperature. The penis moves because of all the blood flowing through it even in a non-erect state. The warmer it is the more heavy and far from the body they'll hang, and we all know about the shrinkage factor when it's cold ;). That being said, an onlooker may perceive these movements as being caused by sexual excitement. I wouldn't concern myself about it but if you think someone around you is uncomfortable when this happens treat it as you would the start of an erection and roll to your stomach or cover up.
My doctor just confirmed this on my last visit. And I would say that be happy when something moves down there.
While it's true that a man's testicles will rise and fall with temperature changes in order to regulate the right conditions for the production of sperm cells, the penis also senses temperature changes triggering it to shrink and shrivel, or expand. Also keep in mind that all that sunshine our bodies are receiving is producing vitamin D which lends a helping hand in the production of testosterone! Warm temperature sensations, and a little boost of testosterone, can sometimes inspire a bit of arousal if nothing more, when taking advantage of nudity and the great outdoors.
Completely normal. Not always what yo may want it do be doing, but there isn't much to do about it. It's much more comfortable to have a fuller flaccid hang of the penis and low swinging scrotum, but you have to adjust to the environment. You may also notice that things will tend to move up and in when you are nervous or exerting yourself. Doesn't this happen to all men?