Where did the time go?

Where did the time go? This is a question I asked during our last discussion on time today. Sometimes the time does go by really quickly while other times it does not. Why is that?

One of the answers that I was given during class was because when we are productive time goes by more quickly while when we are unproductive time seems to stand still. I agree with this answer to an extent. Of course when you are doing something such as listening to a lecture you are engaged in time goes by quickly. However, I come to find that sometimes I feel some of my productive times go by so slowly. This is even includes they things I love.

For example, I love to dance. Sometimes, a two hour dance block seems like it has been 9 hours. Yes, I am having fun but the time does not seem to go by. Why is that? Maybe it's because it is repetitive. Maybe practicing the same day 10 times gets old after a while. However, there are some two hour dance blocks I have that seem like they have only been an hour. I enjoyed both of the dances equally. But why do two dance blocks that are the same amount of time seem to go by faster than others?

I thought an interesting answer to this question was the one Nick mentioned about the stimulus. I hadn't ever thought that the amount of stimulus mattered. It is something I might look into further to understand the concept more.