This is better word to mean density, than Uzito which means weight.
Density, mass and weight are three distinct measures in physics, and since this skill is about science, I would expect the words to be different in Swahili as well. Anything else would be imprecise.
Correct: density, mass and weight are distinctly different, even in Swahili :)
Tungamo or Masi is mass,
Uzigo is weight,
Densiti is density, defined as Tungamo divided by Mjao (volume).