I am teaching Physics and I'm not looking for help for a particular homework problem but on a class. Sorry if this should be in the homework sections. When I park my car where the sun only hits one side and measure my tire pressure later I find the tires on the sun side have a higher pressure. Yet I keep seeing problems where a sealed balloon is cooled solved assuming the pressure doesn't change. It seems to me as the volume decreases the balloon applies less force to the gas which decreases the pressure. If I had a cylinder with a weight on top then I see how the force and pressure would be constant but I don't see how that works with a balloon. Any help would be appreciated.