Dynamics of Exchange Rate Fluctuations between Yen and the US-Dollar

Fluctuations of yen exchange rate to US-dollar are analyzed by a method of classical mechanics. The fluctuations are explained by a linear inhomogeneous differential equation of the second order with a constant coefficient. The inhomogeneous term is an external force. Using a method of the least squares, we determine a polynomial expression of the external force. It is known that the depreciation of yen is caused by decreasing of the external force toward its minimum.