# Intensive gas variables problem

1. May 23, 2012

### cooper607

i just came to learn that the intensive gas variables like pressure and temperature don't depend on the system size. now suppose , i sliced out a gas container into an imaginary plane and i got the extensive variable of volume and internal kinetic energy to be halved..
but why shouldn't the pressure be halved down too as the number of gaseous molecules are decreasing simultaneously with the slicing!!!
well, i understand the pressure is created by collisions of the molecules on the container walls, so please clarify me the concept why the pressure should not be changed in this case??

regards.

2. May 23, 2012

### tiny-tim

hi cooper607!

yes, pressure is created by collisions of the molecules on the container walls,

but they're nowhere near your imaginary plane, so why should that make any difference?

(do you have an equation for this which is confusing you?)

3. May 23, 2012

### nasu

So you think that if you take an empty bottle and you close it with a cork, the pressure inside will decrease??

Your confusion may come form the fact that the pressure depends on the concentration of molecules and not on the total number of them. This is why it is an intensive parameter.