7. As shown in the figure, construct the inscribed circle $\odot O$ inside the square $A B C D$, tangent to $A B$ at point $Q$ and to $C D$ at point $P$. Connect $P A, P B$ to form isosceles $\triangle P A B$. Rotating these three figures (the square, the circle, and the isosceles triangle) around their common axis of symmetry $P Q$ for one full revolution results in a cylinder, a sphere, and a cone. The ratio of their volumes is $\qquad$ .
7. $3: 2: 1$ Let the side length of the square be $2a$, then $V_{\text {cylinder }}=S h=\pi a^{2} \cdot 2a=2 \pi a^{3}$, $V_{\text {sphere }}=\frac{4}{3} \pi a^{3}, V_{\text {cone }}=\frac{1}{3} S h=\frac{2}{3} \pi a^{3}$.

Therefore, $V_{\text {cylinder }}: V_{\text {sphere }}: V_{\text {cone }}=2: \frac{4}{3}: \frac{2}{3}=3: 2: 1$.