The log will float on the water because his density is lower than the liquid, so it will stay at the top due to Archimedes' principle.
Archimedes' principle is a physical law that describes the upward force (the vertical thrust) experienced by any body immersed in a fluid (liquid or gas). This force is strongly related to the density of both the fluid and the body.
You can try the experience at home, by using an object that has a lower density than the water like the sunflower oil, you will see that it will stay at the top of the water too.
