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How far will you slide if you fall off a skateboard?

  1. Jan 24, 2004 #1
    the question is the topic, but im sorri i don't have any numbers i can deal with, because we're just supposed to demonstrate that we understand how we solve htese porblems. unfortunately, I don't. could anyone just give me random numbers and tell me how to olve this question? thanks. im gussing it involves frictiona dn all... any suggestions?
  2. jcsd
  3. Jan 24, 2004 #2
    Easy this one...

    Scientists do experiments don't they? Borrow a skateboard and protective gear, and go skateboarding. Take a tape measure and get some data. This is a FAR better method than making many, many assumptions and then trying to calculate something.

    Then analyse your data and make some conclusions.
  4. Mar 28, 2004 #3
    i know this is an old post, but just remember about the surface of the ground you are sliding on, combined with the part of you or your pads you are sliding on. This is a variable of friction and your momentum. Also, your center of mass upon the fall (beginning of the slide) will help govern your rate of decceleration. If you are on your knees at the beginning of the fall, you will slide farther, if you are on your feet at the beginning of the fall and your body slams downward, your slide will be shorter and therefore excert more impact force (upward) on your body. Hopefully, you will not slide at all and instead conserve your potential sliding energy by putting in some work (combined with cat like reflexes) and roll your body to a hault, injury free.
  5. Mar 28, 2004 #4
    The furthest I ever slid after falling off a skateboard was about eight feet in shorts on rough asphalt scattered with pebbles and a little bit of broken glass when I was 12 years old.
    The result was a chewed up nasty right thigh (about 1 foot long and 5 inche wide road rash) that remained there for about 6 months.
    I was travelling down a 23° (approximate) downgrade at probably 20 mph.
    At the time I weighed no more than 98 pounds.

    The high friction of the ground was counteracted by my light weight, high rate of speed, narrow angle of approach (I hit a rock and was thrown forward a good 5 or 6 feet before making contact) and the relatively low friction of my bare thigh.
  6. Mar 28, 2004 #5
    interesting to think about how your fall might have had worse consequences if you were actually going 10 mph instead of 20mph due to the increased ratio of your speed=directional momentum(forward) vs. gravitationally induced road impact potential energy....
  7. Mar 28, 2004 #6
    Delta x = [tex]v_o t - 1/2at^2[/tex]

    a = coefficient of sliding friction times g

    Total stopping distance is inversely proportional to the coefficient of friction, and proportional to the square of the initial velocity. Ask adrian, he checks this occasionally. I was thinking of putting an odometer on my face shield. Boy.. friction is hot ain't it?
    Last edited by a moderator: Mar 29, 2004
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