What is meant by "no gas enters or leaves the cylinder"? I have the following question. A platform is supported on a piston by compressed air in a cylinder. The mass of the platform and equipment being lifted is 1100kg. The pressure needed to support this mass is 800kPa, and it rests initially at a height of 0.5m. The pressure supply is closed so that no gas enters or leaves the cylinder. One of the pieces of equipment with a mass of 50kg is moved o the platform. The entire system is at room temperature (300K) I am confused with the significance of the bolded line. I'm not sure whether it's implying constant volume, constant pressure, temperature, etc. Can someone explain this?