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What are the physics of stepping at a normal speed but quietly?

  1. Sep 6, 2011 #1
    I've been trying this out to distract people less. Yesterday I took it to a treadmill. It was nearly silent compared to the thuds I'm used to hearing with each footstep. At first I found it easiest to achieve this effect by stepping pretty much only with the balls of my feet. Then I found that I could bring my foot down beginning with the balls but smoothly coming down further later in the step to achieve even greater silence.

    It made my calves sore.

    What are the physics of this phenomenon? The first thing I thought of was 'impedance match' (don't ask me why).
     
  2. jcsd
  3. Sep 6, 2011 #2

    Drakkith

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    It's just easing your foot down instead of slapping or stomping it down like you do during your normal walk I think.
     
  4. Sep 6, 2011 #3
    But how is the transfer of energy different between easing the foot down and the normal walk?
     
  5. Sep 6, 2011 #4

    Drakkith

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    I believe it is simply that you are putting a small portion of your foot down and "rolling" the rest of it down to the floor instead of hitting heel first and slapping the flat part of your foot down. And putting your foot slowly to the ground means you aren't "falling" to the ground with each step like you usually do, reducing the energy of the impact. Kind of like putting a dumbell down on the ground gently compared to dropping it from 6 inches.
     
  6. Sep 6, 2011 #5
    So the energy doesn't get transferred all at once.
    Okay. That probably is better for my bones.
     
  7. Sep 6, 2011 #6
    mainly the knees, coming down hard will wear out the catiledge seperations in your knee joints also the shockwaves can also injure your back and spinal column your far better off if you can use the natural flexibility in your joints to reduce those shock waves on your system. Key example is the cushioning pads in shoes designed for ppl with problem feet or chronic joint and back pains. Coming down softly is far better for your health particularly if you train yourself to alwys do so even when your not thinking about it.
    Coming down softly while running on your balls of the feet and keeping your knees slightly flexed instead of straight will greatly reduce the risk of damage and should be practiced while walking and running. If you do it right you will also find it easier to control and regulate your breathing while running
     
  8. Sep 6, 2011 #7
    The longer the impact time the more the force is dispersed and therefore less noise. The impact time starts when the ball of the foot first hits the ground and ends when the heal hits the ground. A short impact time (hit the ground flat footed) means higher deceleration and therefore more force on contact with the ground. A long impact time (ie. ur calf muscle cushions ur foot) means a lower deceleration and therefore less force on contact with ground. F=dp/dt=ma is the best way to describe it. You can see that F is proportional to 1/t :). If you want me to elaborate on anything just ask... and also if anyone has anything to add or change with my explanation let the OP know :)

    Now just by intuition a harder force will tend to make more noise and a softer force will make less noise. Also, like you said, the more you use your calf muscle to cushion the impact the better for your joints ect. That's why you've got sore calf muscles.

    P.S there is a way to equate energy to dp/dt. I cant remember it but if someone could help out it would be great
     
  9. Sep 7, 2011 #8
    Walking abnormally like this is not advisable. It's probably bad for your leg muscles and joints and feet (particularly achilles heel) in the long term.

    I'm not saying tiptoe-ing about once in a while will do harm, but it sounds like a bad habit.

    Edit: You cause more problems when you think how you walk as opposed to not thinking about it (in general). However ifyou want to perfect your running technique then that's slightly different. Ask a physio or someone in the gym
     
  10. Sep 7, 2011 #9

    sophiecentaur

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    The 'natural' way you were running is probably the most efficient for you - which could be partly why you felt the unpleasant effect. There is a lot of energy return from your tendons (like you pay tens of quid for in posh trainers) when you run normally and we have evolved the hardware and our way of using it. Running in a way that makes you quieter could well be using a lot more energy in the long run (haha).
     
  11. Sep 7, 2011 #10
    yeah you will use more energy... basically because it is unnatural, so you need to think about your movements
     
  12. Sep 7, 2011 #11
    what does the 'p' in dp/dt stand for?
     
  13. Sep 7, 2011 #12
    "p" stands for linear momentum . d is delta or small change. Formula is rate of change in linear momentum or force which is change in linear momentum upon change in time . F=dp/dt is true for all conditions.

    It is basic formula which explains Newton's second law.
     
  14. Sep 7, 2011 #13
    So if you imagine my foot moving in a straight line toward the ground, the change (d) in its linear momentum (p) over time (t) is the force (F) of the impact; so the longer it takes for the impact to occur, the less intense the force of the impact. Force equals mass*acceleration (ma), so the force of the impact is equal to how much the vectors of the atoms in me and the ground change due to the interaction of their electrostatic fields (and whatever else is involved in the interaction of atoms during a collision of the objects that compose them).
     
  15. Sep 8, 2011 #14

    A.T.

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    I think you have it the wrong way around. Landing on your forefoot first is the natural way to run. All fast animals run like this and humans running barefoot do as well. Try to run barefoot hitting with you heel first and you will feel the pain soon. Humans have invented shoes with cushioned heels that allow them to run in an unnatural way (heel strike first) without instantaneous pain feedback. But in the long term it is probably better for your joints to reduce the impact peak forces by landing softly on the forefoot.

    Bad for muscles? When you change your running style they will hurt initially. That means they are adapting. That is what they are made for.

    See also:
    http://barefootrunning.fas.harvard.edu/Nature2010_FootStrikePatternsandCollisionForces.pdf
     
    Last edited: Sep 8, 2011
  16. Sep 8, 2011 #15
    Ah, I can't argue with you there. A physio at a gym has shoes which are made from rubber and fir to the shape of your foot, but it's almost like running barefoot. He says that shoes are unnecessary and that running barefoot is the "proper" way to walk. He was promoting his mate's shoe company, but still, the idea behind the shoe seemed genuine (complex mechanisms of joints, muscles and bones in the leg, foot and back) and seemed to make sense.
    Of course this shoe will not work for all people, but I imagine it would for most normal healthy people.
     
  17. Sep 8, 2011 #16
    First part spot on! BTW if u didnt know already, momentum = mass x velocity. Second part, if i read correctly sounds OK, could be worded better lol. The force on impact basically relies on how quickly (or slowly) your foot slows down to zero velocity (ie the acceleration). F=ma, high acceleration, high force. F=ma and F=dp/dt are equivalent, so your first and second parts are describing the same thing just using equivalent terminology.

    Edit: And yes the intermediate force is the electrostatic force b/w electrons in your foot and the electrons in the ground
     
  18. Sep 8, 2011 #17
    I think you have it the wrong way around. Landing on your forefoot first is the natural way to run. All fast animals run like this and humans running barefoot do as well. Try to run barefoot hitting with you heel first and you will feel the pain soon. Humans have invented shoes with cushioned heels that allow them to run in an unnatural way (heel strike first) without instantaneous pain feedback. But in the long term it is probably better for your joints to reduce the impact peak forces by landing softly on the forefoot.

    I agree with this post Humans are famous for developing bad habits. It does not take much effort to learn how to correct running habits. I have run marathons and I found that once I learned how to regulate breathing and lower shock the amount of strain on the body was significantly reduced. My times improved on average by 50% of the original and I am no where near as sore or exhausted after words. The thump thump thump of long distance running is nothing compared to the bit of concentration on safe running habits. Shock absorbing the blows can only be more healthy than the thump thump thump. After al its a a natural action to lift heavy objects with the back instead of the knees. Learning to properly absorb shock requires the same amoutn of concetration. YOu can always hear what your feet is doing when they land. When it starts sounding louder correct your landings its that simple.
     
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