Changes

[[File:Centre_of_mass_train.png|right|300px|link=https://www.amazon.co.uk/gp/product/B001ELZ6F8/ref=as_li_tl?ie=UTF8&camp=1634&creative=6738&creativeASIN=B001ELZ6F8&linkCode=as2&tag=nrjc-21&linkId=91947c71f7b82fcaf986f96327cd542d|thumb|It was essential to find the '''centre of mass''' of an old steam train trains to make sure it was low enough that it wouldn't tip over on the tracks at a turn. To do so they hung the entire engine from the ceiling from different points and drew chalk lines directly down from those points. There are two points of intersection where the '''centre of mass''' was found. One when the boiler was empty and one when it was full.]]