A balloon does not rise indefinitely because :

1. the density of air increases with altitude
2. the density of air decreases with altitude
3. the weight of the displaced air increases.
4. None of the above

When a fish has to rise up in water, it diffuses oxygen gas from its blood into the bladder, so its volume …………… and its average density …………… .

1. decreases, decreases
2. increases, decreases
3. decreases, increases
4. increases, increases

When a piece of wood is suspended from the hook of a spring balance, it reads 70 gf. The wood is now lowered into water. What reading do you expect on the scale of spring balance?

[Hint: The piece of wood will float on water and while floating, apparent weight = 0].

How does the density ρ_S of a substance determine whether a solid piece of that substance will float or sink in a given liquid of density ρ_L ?