How does a bike helmet protect our head ?

Explanation

A bike helmet protects our head using two simple principles of physics :
(i) The foam lining in the interior of the helmet increases the time over which the impulse acts , reducing the force thereby (lmpulse = force `xx` time = constant ).
(ii) The rigid helmet spreads this force ,applying it over a wider area . Therefore , pressure exerted (= force/area ) is reduced . As is know , it is the applied pressure that breaks the bones and the skin , rather than applied force .