1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: How to make successful helmet from scratch

  1. Apr 20, 2015 #1
    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown >

    We have to make a helmet in engineering class that will survive a bludgeoning from the teacher with a hockey stick. Im not sure what the best materials to use would be or the best way to make it. Additional info is that we are trying to make a helmet for rugby that will be safe.
    Last edited by a moderator: Apr 20, 2015
  2. jcsd
  3. Apr 20, 2015 #2
    Any constraints to the design? You could go Dark Helmet, that would certainly be safe (but obviously rather impractical).
  4. Apr 20, 2015 #3
    One important aspect to overview is the impulse. You should try to have a dampening in the helmet so the force is spread out over time. From there you could look at different foams or other materials with low weight.
  5. Apr 20, 2015 #4
    only restraints are the outside has to be paper machete (to add decoration) the helmet has to protect a watermelon
  6. Apr 20, 2015 #5
    The thing to optimize in the helmet will be the deceleration of the head. So, to some degree you will be bound by very basic physics. E.g. if the helmet is of thickness d, the smallest deceleration from speed v will be a continuous declaration across that distance d, the deceleration given by

    a = v^2/(2s)

    So, on the one hand you're looking for a material that will compress linearly under such deceleration, but at the same time you're also looking for a material that will distribute a sharp impact across the head area (so you don't get impaled by something). Those two are somewhat opposed to each other.
  7. Apr 20, 2015 #6


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    There are three things a helmet needs to do.
    As others have noted, you want the impulse spread as evenly as possible over time. An elastIc material won't do that well because the resistance increases linearly with compression. A material that yields plastically is better, offering a more or less constant resistance as it collapses. The tricky part is that you need to get the resistive force right. Too high, and too much force will be transferred to the head, too low and it will collapse completely before enough of the blow has been absorbed. So the ideal is a resistance just a bit less than the natural strength of what you are trying to protect - in this case, the tissues that hold the brain together.
    As also noted, you need to be able to cope with a blow from a sharp object. That implies a strong and stiff outer shell.
    The third is to spread the blow evenly over an area of the skull so as to avoid localised crushing, so a softer lining (but this is the least important of the three).
    As regards onslaught by the teacher, an Apprehended Violence Order should also be effective. Consult your lawyer.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Threads for successful helmet scratch
No. of trials for P>0.99 of at least one basket ball success