Archimedes Principle: The buoyant force on a submerged object is equal to the weight of the liquid displaced by the object.

Buoyancy is a combination of weight and displacement.

Two vessels will have the same buoyancy if they are the same exact shape and weight. For example, if you were to place two identical Tupperware bowls in water and fill one with 6 oz. of lead and the other with 6 oz. of feathers they would displace the same amount of water. If you add 6 oz. more material to one of the bowls, the water line would then change. The water surrounding the bowls doesn’t care what’s inside the bowls. With two objects of exactly the same shape, it is their difference in weight that will determine the floatation.

Let’s say you were sitting in a boat in a pool with a large rock inside of the boat and you were to toss the rock out of the boat into the pool. The boat now sits higher on the water and the water level of the pool lowers. When placing the rock which has little displacement into the pool, it lowers the pool’s water line because the rock displaces only its volume. While the weight of the rock was in the boat the rock displaced its total weight, so the boat displaced much more water, raising the level of the pool’s water line.

• Buoyancy is a concept that can be difficult to comprehend at times. However, with a simple consideration of forces it can be made clear.

• The buoyant force is a consequence of the variation of pressure with depth.

• The pressure on the bottom of the object is larger than the pressure at the top.

• This leads to a net upward force on the object.

• If this upward buoyant force is larger than the weight, then the object floats!

• The difference in the weight of two vessels with identical shape will determine the difference in how high or low they float.

• The difference in the shape of two vessels weighing the same will determine the difference in how high or low each floats.

• If they have the same weight and shape, they will float the same, no matter what material they are made of.

So you can fill it helium and as long as the weight does not change, it floats the same.