Show Me Some Science! Buoyancy

The Little Shop team experiments with putting different objects in different fluids and seeing which float. Helium filled bubbles in the air and granite in mercury metal! Does it float?

What’s Happening?

When an object is placed in a fluid, the fluid pushes up on the object. This force is called buoyancy, and it happens in any fluid: water, mercury metal, and even air! Bubbles are made of mostly air, and so their buoyant force is similar to their force of gravity and they hang out in the air for a long time.

Sometimes the buoyant force on an object is enough to cause it to float in the fluid. Things will float in a fluid if they are less lighter than an equivalent amount of that fluid. This is called density, which can be found by taking mass and dividing it by the volume it occupies. Denser objects feel a stronger force of gravity pulling them down, and since they cannot occupy the same space as other objects, this causes a buoyant force on the less dense objects.

You have seen this before, in helium balloons. There’s nothing intrinsically floaty about helium, it’s just that it’s lighter than air and it is therefore buoyant.