Proton beams have been colliding at 7 TeV in the Large Hadron Collider (LHC) since 30 March 2010, meaning that the LHC research programme is underway. Particle physicists around the world are looking forward to using the data from these collisions, as the LHC is running at an energy three and a half times higher than previously achieved at any particle accelerator. There are some important questions to be answered by the LHC experiments. What is the origin of mass? What is 96% of the universe made of? Why is there no more antimatter? To avoid colliding with gas molecules inside the accelerator, the beams of particles travel in an ultra-high vacuum--a cavity as empty as interplanetary space. The internal pressure of the LHC is 10[superscript -9] Pa, one hundred times less than the pressure on the Moon! The aim of this article is to introduce a few simple physical calculations about some physics phenomena related to pressure that take place in the LHC, so that they can be directly used in the secondary school classroom and stimulate the students' interest in the greatest experiment in history. (Contains 2 figures.)