gravity
Weight is a measure of the force of gravity pulling down on an object, whereas buoyant force pushes up on an object. Which force is greater determines whether an object sinks or floats. Look at the Figure below . On the left, the objects weight is the same as the buoyant force acting on it, so the object floats. On the right, the objects weight is greater than the buoyant force acting on it, so the object sinks.