I recently posted a question about solids that led to a very productive discussion about solids, weight, gravity and pressure. I learned that many intuitive ideas I had about these concepts were wrong and I now have a better understanding as a result. However, in the course of my reading I came across the buoyant force. Now of course at a general level I know what buoyancy is, but after reading a number of sources it became apparent that it’s much more complicated than I thought. I now think I have a fair understanding of this force, but there are a few things I can’t get straight in my head, even after reading a lot. Here’s my understanding, followed by my question. These points are at a very simplified level – that is, a homogeneous liquid, in this case water, with all other forces removed. I am talking about a static situation so I am disregarding flow, drags, and other complicating factors. 1. A submerged object displaces its volume in water. 2. The weight of the water displaced is equivalent to the upward buoyant force on the object. 3. The buoyant force arises from the difference in pressure between the top of the submerged object and the bottom of the submerged object. 4. The pressure in a column of water increases with depth and hence the buoyant force will increase with depth, all other factors remaining equal. 5. The apparent weight of a submerged object is reduced by the magnitude of the buoyant force. Because weight is a force, the net force applied to the object is the difference between its weight and the buoyant force. 6. If an object’s apparent weight is greater than the buoyant force, the object will sink. And vice versa – if less than the buoyant force, the object will rise. The total apparent weight of a container of water and an object outside of the container of water is the sum of the two weights. If the object is placed in the container of water, the total weight of the container and water is increased by the weight of the object. However the apparent weight of the object, inside the container, is reduced by the buoyant force. Assuming that the object’s mass and shape is such that the buoyant force is exactly equal to its weight and the object does not sink, the object’s apparent weight in the container will be zero. However, the total system weight of container, water and object is increased by the weight of the object. What is happening here? The upward force exactly balances the downward force, yet there is still a nett downward force.