Helmet
Soldiers wear steel helmets to protect their heads from explosions and flying bits of metal.  Construction workers wear plastic helmets to protect their heads from falling objects.  Welders wear special helmets with a dark window that lets less light through.  This protects their eyes from the bright light of welding.  People who ride bicycles or horses wear plastic helmets with foam, to protect their heads in case they have an accident.  Motorcycle riders wear similar but stronger helmets.  People who rock climb wear helmets in case they fall.  Cavers wear helmets to protect their heads from bumping into rocks in a cave.  Helmets are also worn for protection by participants of numerous sports including horse racing, baseball, ice hockey, and cricket.