DETERMINING THE ENERGY REQUIRED BY WATER IN A ROLLING CYLINDER EE ABSTRACT Milla Mouhu In this research the effects of a rolling cylinder containing water were investigated from the point of view of energy conservation. A tin with various masses of water inside was rolled down a small incline and the time was measured. Qualitative and quantitative analysis of the results is done and total amount of energy that water requires is obtained for different masses. This total energy was solved subtracting kinetic energies of the tin and work done by resisting forces from the initial potential energy. One of the sources suggests that a "gum model" would predict the results where the behaviour of water would be similar to a solid object stuck in the wall when small amount of water was in the tin. Research question was therefore formed to be as follows: How much do different amounts of water, inside a cylinder rolling down an incline, require energy and to what extent is the gum model a reliable method in calculating that energy? Total amount of that energy is relatively high with small masses where as predictions of the gum model follow another path leaving a great difference between those results. Results were quite remarkable since the gum model was proved to fail with small masses and succeed with greater masses. It was concluded that the gum model cannot be applied for quantitative experiments and therefore a better model or an explanation should be discovered.