Whether the object floats or not is dependent on two forces. The force of gravity acts downward on the object, while an upward buoyant force is exerted by the liquid. If the force of gravity is greater than the buoyant force, the object will sink. If the buoyant force is greater the object will sink. When the forces are equal the object will hover in the water. The buoyant force is always upwards since the pressure in a fluid increases with depth. As a result the upward force on the bottom of an object is greater than the downward force on the top of an object. Another way to look at buoyancy is Archimedes' principle, which states, "the buoyant force on an object immersed in a fluid is equal to the weight of the fluid displaced by that object" (263 Giancoli).
So will the cheese log float or sink? That depends on whether or not the weight of water displaced by the cheese log is greater than the weight of the cheese log. Click on the link to find out.
Here's another link that explains buoyancy in more detail.