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G Force equivalencies (help and idiot out)

  1. Dec 23, 2007 #1
    OK. Basically the only thing I know about physics is the definintion and I have a question about some electronic gear that I own. I figured that the best place to get the answer would be a Physics board since the manufacturure doesn't list this information anywhere. So...here is a little story problem for all of you who want to help.

    I have an iPod. It contains a hard drive that is rated up to 1500Gs/1.0ms. The iPod itself weighs 140 grams. Let's say the thing fell about three feet onto a thin area rug. The thing works fine, but, approximately how many Gs would you estimate this thing experienced?

    OR put another way, given the weight of the product and the shock rating of the unit, what is the real world equivalency of 1500Gs? I read that for a compact flash card, 2000Gs is equivalent to a 10 foot fall.

    Any takers? I look forward to any responses!!!

  2. jcsd
  3. Dec 23, 2007 #2


    Staff: Mentor

    Hi Jason, welcome to PF. There are two important questions, how high is it falling, and how short is the stop. In other words, on a rug there is some cushion, on a wood floor there is less, and on concrete there is even less. The 1500 G rating means that it can fall 1500 times further than the stopping distance. So, if you fall 1.5 m then it can survive a 1.5m/1500 = 1 mm stopping distance. That will be fine on a thin rug, but probably not on concrete.
  4. Dec 23, 2007 #3

    Thanks for the reply. The fall was from off the futon (by now you have guessed this really happened!)

    Anywhoo, the distance from the surface of the futon to the floor is approximately 3 feet. The rug it fell onto is one of those berber style area rugs placed on a hardwood floor. One thing that may have made things better for the little guy was that it was attached to the headphones. I am thinking that near the time of impact the headphone wire lessened the impact. I have no way of knowing because I was sound asleep!

    I feel like this is a Car Talk problem and I can hear those two auto guys laughing and hee-haw-ing as I type this. But, thanks so much for your help in the matter! From your guestimates I am pretty sure it is going to be fine. If you have any other input I'll be eagerly awaiting any input!

  5. Dec 23, 2007 #4


    Staff: Mentor

    Yes, it should be fine. 3 feet / 1500 is less than 1/32". With a berber rug being at least 1/2" thick it should survive even if the floor underneath were concrete.

    Of course, the solid-state type should be even more impact resistant. Since I have young kids I got a solid-state one for exactly that reason.
    Last edited: Dec 23, 2007
  6. Dec 24, 2007 #5


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    Staff: Mentor

    You can use newton's laws of motion to calculate the speed based on a certain height, then estimate the g's based on how thick the carpet is (ie, how far it goes while decelerating). It won't be exact because with a carpet it won't be a uniform force, but it'll give you a ballpark estimate.
  7. Dec 24, 2007 #6

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    Homework Helper

    This specification of G rating is new to me. Could you just elaborate a bit on this? Ultimately it means that the g force during braking should not exceed a certain maximum value, right?
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