Why does an increase in money in circulation increases price levels? I'm a physics student who likes economics very much. I'm trying to get a simple explanation for inflation. I hope that there is one that doesn't involve people willingly rising prices. Thank you very much!
new money is created; it belongs to somebody.
that somebody can either save/invest the money, or spend it on consumption.
provided at least some of the money is spent on consumption, the demand for consumer goods increases.
in a competitive market, this increase in demand results in an increase in the price level. (Note that the sellers are not "willingly rising prices" because, in this simple model of competition, sellers take the price a given natural consequence of the interaction of supply and demand).




You might also find it interesting to read about the quantity theory of money.