In Japan, the population of the aged people became larger and larger recently. The probability of fall among them is higher than young people because of declining of physical ability. Therefore, it is obvious that fall is very important problem and its prevention has been studied for a long time. However, most studies have not been done from the theoretical view. In this study, we conducted to investigate the situation of fall using rigid body model. We calculated the velocity just before colliding with a floor. Furthermore we considered the condition where the body slips by calculating the constraint force such as normal force and friction force.
