Why do oil and water return to separate layers after shaking?
A tightly closed oil-and-vinegar dressing jar turns cloudy when shaken, then slowly returns to a gold region and a watery region on the table.
Talk about it
- Before shaking anything, ask what is changing: the molecules themselves, the droplet size, or both?
- At the gate, consider all three possibilities—plain jar, soap jar, or together—before advancing the shared clock.
- After the reveal, ask which observation showed a change in droplet reunion rather than a change in density.