Question: why is the process of chemiosmosis also called a proton motive force

title: Chemiosmosis
text: Δ μ H + = F Δ ψ + R T ln ⁡ ( H + ) N ( H + ) P = F Δ ψ − ( ln ⁡ 10 ) R T Δ p H ( \ displaystyle \ Delta \ ! \ mu _ ( \ mathrm ( H ) ^ ( + ) ) = F \ Delta \ ! \ psi + RT \ ln ( \ frac ( ( \ mathrm ( H ) ^ ( + ) ) _ ( \ text ( N ) ) ) ( ( \ mathrm ( H ) ^ ( + ) ) _ ( \ text ( P ) ) ) ) = F \ Delta \ ! \ psi - ( \ ln 10 ) RT \ Delta \ mathrm ( pH ) ) A