By the formula PV/T = PV/T, If there is a piston, and it compresses, so the volume gets smaller, the temperature will go down too.. But, I think if the volume gets smaller, the space is smaller, so the gas particle will collide more frequently, which makes the temperature goes up. And, my logic breaks what formula says. I really have no idea what actually V/T = V/T says. And, I want to know what pressure really is on gas particle. Is it the force given by a gas particle to another per the gas particle area? Or, is it the pressure given by gas particles to the piston ?? If the piston compresses, will the pressure also get bigger?