How does the food coloring spread when you put dish soap on a Q-tip?

The food coloring spreads when you put dish soap on a Q-tip due to a phenomenon called the Marangoni effect.

Here's an explanation of the process:

1. Surface Tension: Liquids like water have a property called surface tension, which causes their surface to behave like a stretched elastic membrane. In this case, the surface of the water is covered with food coloring.

2. Dish Soap Disrupts Surface Tension: When you dip a Q-tip with dish soap into the water, the dish soap molecules start to spread on the surface. These molecules disrupt the surface tension of the water, causing it to weaken.

3. Marangoni Effect: The Marangoni effect is the movement of a liquid caused by differences in surface tension. In this case, the area where the dish soap is present has a lower surface tension compared to the surrounding water. This difference creates a gradient in surface tension, causing the water to move away from the area of low surface tension.

4. Spreading of Food Coloring: As the water is pushed away from the Q-tip, it drags along the food coloring molecules present on its surface. This results in the food coloring spreading in a circular pattern away from the Q-tip.

The process continues as long as there is a difference in surface tension between the area with dish soap and the surrounding water, causing the food coloring to spread further.