Shaking salad dressing and rain forming both represent physical changes because there is no creation of new substances, just a reversible alteration of their physical state.
Both shaking up salad dressing and rain forming in a cloud are examples of physical changes because they involve reversible alterations in state without changing the substances' chemical identity.
Shaking salad dressing typically involves emulsifying oil and vinegar, which do not chemically react but mix temporarily. When rain forms in a cloud, water vapor condenses into liquid droplets. Both processes are instances where physical properties change but substances maintain their chemical structures. These are classic examples of physical changes since the molecular composition of the involved substances remains unchanged. Moreover, both instances are examples of reversible changes because the mixed salad dressing can separate again, and condensation is the reverse process of vaporization which happens when liquid water evaporates back into water vapor. No new substances are created in either process, distinguishing these changes from chemical changes, where new substances with different properties would result.
Therefore, shaking up salad dressing and rain forming in a cloud hold in common that they are both reversible physical changes, not involving a change in chemical composition.