Answer to Question #80957 in Physics for Kacey

Question

What effect would an air bubble in modelling clay have on calculating density?

Answer 1

Density can simply bs expressed as
ρ=M/V,
where
M – mass of the clay,
V – volume of the clay.
Average density of wet modelling clay is about 1760 kg/m^3. It means that 1 m^3 of wet clay without air bubbles or any other inclusions will weigh 1760 kilos. Average density of air is about 1.25 kg/m^3 – much less than clay’s density. So if we take 1 m^3 of clay with air bubbles inside, it will decrease overall density.
Show it by taking the same volumes V of clay without bubbles and of clay with bubble (remember that in this case V_clay=V-V_air). We have:
ρ_1=M_clay/V,
ρ_2=(ρ_clay·(V-V_air)+ρ_air·V_air)/V.
We see that the same volume of clay with the air bubble weigh less than this volume of clay with no bubble, or
ρ_2<ρ_1.
Answer
An air bubble in modelling clay would decrease overall density