Smith chapter 1 problem 5,  Materials for protective sports helmets

 

a)      Important criteria include

 

 

b)      Materials satisfying the above criteria:

 

c)      Solid metal is not a good choice because it would be way too expensive.  One could, for example make the outside of a football helmet out of aluminum alloys, but it would cost a lot.   And still one would need a foam rubber or soft plastic liner.