When long dry hair is brushed the strands often move away from each other because while brushing

When long dry hair is brushed, the friction between the brush and the hair strands causes a transfer of electrons, a phenomenon known as the triboelectric effect. This process results in the hair strands acquiring the same type of electrical charge, typically positive for human hair [1]. According to the fundamental principles of electrostatics, objects with similar (like) charges exert a repulsive force on each other [1]. Consequently, each individual hair strand attempts to move as far away as possible from its neighbors, causing the hair to 'fly away' or stand up. Dry conditions exacerbate this effect because moisture normally provides a path for these static charges to dissipate. Other factors like air movement or gravitational changes are negligible in this context, as the primary force driving the separation is the electrostatic repulsion between the similarly charged strands.

Sources

1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 5: Exploring Forces > Activity 5.7: Let us experiment > p. 71