Boyle's law states that the volume of occupied by a fixed mass is inversely proportional to the pressure, provided temperature is constant . mathematically expressed .V = 1 /p K = k /p PV = K , where K is constant.P¹ V¹ = P² V² = P³ P increases as V decreases and as V increases P decreases. In terms of kinetic theory , when gases are heated at constant pressure , the molecules gain kinetic energy ( K.E ). They move faster and so the average momentum change molecules on impact with the walls is the same as before. Thus , the volume increases so that the molecules have to travel further between collision and the wall, i.e successive impacts.