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imron07

At what direction is the frictional force?

  • one year ago
  • one year ago

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  1. imron07
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    • one year ago
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  2. BTaylor
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    The frictional force is parallel to the surface, opposing the motion. So, it would be pointing down the slope, if the drawing in the arrow represents the motion.

    • one year ago
  3. imron07
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    Yes, the arrow represent the motion. But ummm, i'm not sure the frictional force is parallel to the surface, opposing the motion. Just like when we walk, the frictional force is in the same direction as our motion....

    • one year ago
  4. BTaylor
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    No, it's not. The friction always opposes motion.

    • one year ago
  5. RaphaelFilgueiras
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    |dw:1348327921150:dw|

    • one year ago
  6. RaphaelFilgueiras
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    |dw:1348328024524:dw|

    • one year ago
  7. BTaylor
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    the friction force reduces the acceleration of the object. When you are walking, the friction between your shoe/foot and the ground keeps your foot from sliding forward indefinitely.

    • one year ago
  8. RaphaelFilgueiras
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    |dw:1348328081329:dw|

    • one year ago
  9. imron07
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    @BTaylor yes, it oppose the motion, but the motion of our shoes.

    • one year ago
  10. RaphaelFilgueiras
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    the a point is moving in rotation direction so frictions force oppose it

    • one year ago
  11. RaphaelFilgueiras
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    that's why the car can rise rump

    • one year ago
  12. RaphaelFilgueiras
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    get @imron07 ?

    • one year ago
  13. imron07
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    @RaphaelFilgueiras : What about this:

    • one year ago
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  14. RaphaelFilgueiras
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    im talking about this

    • one year ago
  15. RaphaelFilgueiras
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    |dw:1348328369452:dw|

    • one year ago
  16. RaphaelFilgueiras
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    |dw:1348328561760:dw|

    • one year ago
  17. RaphaelFilgueiras
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    the friction is opposite to the moviment of weel

    • one year ago
  18. Mikael
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    |dw:1348328592225:dw|

    • one year ago
  19. imron07
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    Yeah, i understand your explanation. But if we apply Newton's law, should we pick that direction too for friction to find system acceleration?

    • one year ago
  20. Mikael
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    the friction is opposite to the moviment of POINT OF CONTACT

    • one year ago
  21. RaphaelFilgueiras
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    yep

    • one year ago
  22. Mikael
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    Yes ma = mgsin alpha + f

    • one year ago
  23. RaphaelFilgueiras
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    f-mgsin(alpa)=ma

    • one year ago
  24. imron07
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    Shouldn't \(mg\sin{\alpha}\) is in opposite direction with friction now?

    • one year ago
  25. RaphaelFilgueiras
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    yes it is opposite

    • one year ago
  26. imron07
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    @RaphaelFilgueiras yes that's what I mean :)

    • one year ago
  27. Mikael
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    NO it is coincident with mg sin alpha : here is why (let me finish pls

    • one year ago
  28. Mikael
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    T|dw:1348328885247:dw|

    • one year ago
  29. Mikael
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    And when wheel is freely rolling the friction acts BACK on it

    • one year ago
  30. RaphaelFilgueiras
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    so your car never will rise the ramp!!!

    • one year ago
  31. Mikael
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    @RaphaelFilgueiras you are wrong : in his picture there are NO OTHER forces. The cart is only rolling up BY INERTIA and of course slows eventually. This is different from motorized climbing up !!!

    • one year ago
  32. RaphaelFilgueiras
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    the car is moving up

    • one year ago
  33. Mikael
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    The point of contact is moving a wee-bit slower than the surface - so the surface ACCELERATES it !

    • one year ago
  34. imron07
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    @Mikael : So only when the engine turned on, friction will directed upward?

    • one year ago
  35. Mikael
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    YES @imron07

    • one year ago
  36. Mikael
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    And pls medal (-s)

    • one year ago
  37. Mikael
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    the vector is velocity. And please admit that I am right @RaphaelFilgueiras

    • one year ago
  38. Mikael
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    Again I clarify : When the wheel is free it serves as a friction-conduit from the surface to cart. When the motor is working the opposite: the wheel transfers torque from cart to surface

    • one year ago
  39. Mikael
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    It is a delicate but DRAMATIC CHANGE

    • one year ago
  40. imron07
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    Well, i understand both of your opinion. But i agree with @Mikael . If the vector I draw is Force, would something change (engine on)?

    • one year ago
  41. Mikael
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    Of course - all is opposite

    • one year ago
  42. RaphaelFilgueiras
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    they are opposite but mg is greater than f

    • one year ago
  43. RaphaelFilgueiras
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    so it will stop,and then the friction and mg will be in same direction

    • one year ago
  44. Mikael
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    This time @RaphaelFilgueiras IS ok. Though he will never admit someone else IS .....

    • one year ago
  45. Mikael
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    The last remark of Raf is WRONG (again!)_

    • one year ago
  46. imron07
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    You mean friction is downward even if the tire's working to move the car upward too?

    • one year ago
  47. Mikael
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    Friction is UPWARD when the tire PUSHES the surface (working) and downward when the SURFACE pushes the tire

    • one year ago
  48. Mikael
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    Both of you should imagine a tiny (really tiny) velocity difference betwee Contact point and surface. It has OPPOSITE directions in these opposite cases !

    • one year ago
  49. imron07
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    @Mikael can you draw it please, (when engine turned on, and another force pull the car too).

    • one year ago
  50. Mikael
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    When wheel PUSHES it is faster downward - so frict is UPWARD

    • one year ago
  51. RaphaelFilgueiras
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    |dw:1348329423502:dw|

    • one year ago
  52. Mikael
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    |dw:1348329805336:dw|

    • one year ago
  53. imron07
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    Okay, I understand now. Thanks @RaphaelFilgueiras & @Mikael !

    • one year ago
  54. RaphaelFilgueiras
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    yw

    • one year ago
  55. Mikael
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    You see the friction force is OPPOSITE to the RELATIVE VELOCITY\[V_{contact} - V_{\text{surface velocity relative \to wheel's center}}\]

    • one year ago
  56. imron07
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    Yeah, that's what in my mind :D

    • one year ago
  57. Mikael
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    @imron07 and @RaphaelFilgueiras : Thank you both for educating me and all of us by your questions and thoughts.

    • one year ago
  58. imron07
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    It was a nice discussion :)

    • one year ago
  59. Mikael
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    DUBITANDO AD VERITATEM PERVENIMUS !

    • one year ago
  60. Mikael
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    Veritas in disputando gignitur.

    • one year ago
  61. imron07
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    What's that last phrase means?

    • one year ago
  62. Mikael
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    http://translate.google.com/#la/en/Veritas%20in%20disputando%20gignitur.

    • one year ago
  63. Mikael
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    http://translate.google.com/#la/en/PERVENIMUS%20DUBITANDO%20AD%20VERITATEM

    • one year ago
  64. RaphaelFilgueiras
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    |dw:1348331561351:dw|

    • one year ago