Buoyancy is also what makes a party balloon and a hot air balloon
rise. Take for example this helium filled balloon. It rises in air
because the density of helium is less than the density of air. This
produces a buoyant force :
which means that I can hang a mass of
from a helium filled balloon with volume, V. Note that in this
calculation I neglected the mass of the thin rubber which
makes up the balloon itself. Solids in air also experience buoyant
forces but because the density of solids is so much greater than the density of gases this is in general a small if not negligible effect. For example the buoyant force on a person is typically less than 1 N.