Question

1. if we wanted to investigate how electrical forces act on polar substances, such as the paint used in the gif, which variables should be changed to produce reliable and useful data?

use the same liquid, but at different temperatures (e.g. cold, room temp, boiling.) to see if that will have an effect on the coatings ability to repel the liquid.
change the fabric/surface that is coated with neverwet to see if that will affect the ability to repel the liquids.
spill different volumes of paint onto the coating to see if some will stick.
use liquids with different polarities, from less to more polar to see the effect the polarity of the liquid has on the neverwet.

Explanation:

The question is about investigating how electrical forces act on polar substances. Electrical forces are related to the polarity of substances. To study the effect of electrical forces (which are influenced by polarity) on the interaction (like repelling) of the coating (NeverWet) with a liquid (polar substance), we need to vary the polarity of the liquid. Changing the temperature of the same liquid (option 1) is about thermal effects, not electrical - force - related polarity effects. Changing the fabric/surface (option 2) is about the properties of the surface, not the electrical forces on the polar substance (liquid). Spilling different volumes (option 3) is about quantity, not the nature (polarity) of the substance. Using liquids with different polarities (option 4) directly relates to studying how electrical forces (which depend on polarity) act on the polar substances (liquids) and their interaction with the coating.

Answer:

Use liquids with different polarities, from less to more polar to see the effect the polarity of the liquid has on the NeverWet.