Sentence:  Seatbelts, airbags, collapsible steering columns, dentable windscreens, <WSD>squashable</WSD> fascias and squashable front and rear ends have all added to safety, but how? To answer that you will need to recall some GCSE physics and learn more formal ways of expressing it &mdash; using equations and graphs. 
Meaning of the word marked with <WSD> tags:  Capable of being compressed or squeezed.