Elastic Collisions When Molecules Hit the Wall of the Container
Gas in a box exerts an outward pressure on its walls. A molecule colliding with a rigid wall has the direction of its velocity and momentum in the x-direction reversed. This direction is perpendicular to the wall. The components of its velocity momentum in the y- and z-directions are not changed, which means there is no force parallel to the wall.
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"OpenStax College, Kinetic Theory: Atomic and Molecular Explanation of Pressure and Temperature. February 4, 2013."
http://cnx.org/content/m42217/latest/
OpenStax CNX
CC BY 3.0.