What is the purpose of the black piece of paper in the experiment with salt and pepper?

The purpose of the black piece of paper in the experiment with salt and pepper is to provide contrast for visualizing movement. When the mixture of salt and pepper is interacted with, typically through methods such as shaking or using static electricity, the black background allows for easier observation of the motion of the particles. The contrasting color makes it clearer to see how the salt and pepper separate or move in relation to one another, which is essential in demonstrating the concept being explored, such as the effects of static charges or the principles of mixture separation. This visual clarity enhances the understanding of the experiment, demonstrating the dynamics of forces at play.