Final answer:
It is advisable not to touch the inside of a canvas tent during rain to avoid disrupting the surface tension of water droplets, leading to leaks. Molecules in a droplet create a tension that adheres the droplet to the tent fabric, which can be imbalanced by touch.
Step-by-step explanation:
When it's raining, it is advisable not to touch a canvas tent from the inside because touching it may disrupt the surface tension of the water droplets on the canvas, causing them to coalesce and possibly leak through. The molecules in a water droplet are attracted to each other, creating a tension that allows the droplet to adhere to the fabric of the tent.
By touching the tent, you introduce an imbalance in these forces, increasing the likelihood that the water will penetrate the canvas. This behavior of molecules is also applicable in different scenarios, such as water forming round beads on a waxed car due to the nonpolar nature of the wax that does not interact strongly with water. In contrast, rain spreads into a thin film on a dirty car because of the attractive interactions between the polar substances on the car's surface and the water, instead of forming beads.