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!

Object and Friction on the object

  1. May 1, 2012 #1
    Good Morning

    I am new user on Forum and I'm sorry for all mistake. I am living in Poland and My English is on the low level.

    My question concers friction on the objects. We have formula:

    [tex]T=μ \cdot N[/tex], where

    [tex]μ[/tex] - coefficient on fraction
    [tex]N=m\cdot g[/tex]

    and formula:

    [tex]F=m\cdot a[/tex]

    I think that:

    [tex]F=T \Rightarrow m\cdot a=μ \cdot m\cdot g[/tex]

    This is true?? Coefficient [tex]m[/tex] is mass object?? If on the object interacts more physical force ( example Friction's ) = [tex]m \cdot a=m\cdot μ\cdot (N_{1}+N_{2}+...+N_{n})[/tex]??

    I greet
     
    Last edited: May 1, 2012
  2. jcsd
  3. May 1, 2012 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    welcome to pf!

    good morning, dexter90! welcome to pf! :smile:

    (btw, we usually write "T" only for "tension" :wink:)

    one object only has one normal force (N), and one friction force (µN) with a particular surface

    for example, if a rope with tension T is pulling an object with mass m along a horizontal surface, then the F = ma equation is:

    T - µmg = ma :wink:

    (your equation ma = µmg is impossible … if the only force is friction, then the object won't move!)
     
  4. May 1, 2012 #3
    Thanks you for quickly answer.

    I understand, one object -> one force ( friction on the surface ). Friction is force which retard object. If on the object interacts more force's then coefficient retard is bigger, example: air resistance, then We have from formula:

    [tex]m\cdot a=m\cdot g\cdot μ[/tex], next

    [tex]a=g\cdot μ + \lambda[/tex], where:

    [tex]\lambda[/tex] - coefficient air resistance in [N].

    Yes?

    I greet.
     
  5. May 1, 2012 #4

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    hi dexter90! :smile:
    not exactly …

    air resistance is not proportional to mass (it's proportional to cross-section area, and it also depends on speed, but not mass, see http://en.wikipedia.org/wiki/Drag_equation),

    so the equation will be something like -ma = µmg + kAv2,

    or a = -(µg + kAv2/m) :wink:
     
  6. May 1, 2012 #5
    :)

    I have a question to this formula:

    [tex]-ma...[/tex]

    Not exist [tex]-[/tex] in [tex]ma=μmg[/tex]. Now, it is present because force air resistance is returned in the opposite direction??

    I apologize for the grammar :)
     
    Last edited: May 1, 2012
  7. May 1, 2012 #6

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    both the friction and the air resistance are retarding forces (they both reduce the acceleration of a moving object)

    so it should have been -ma = µmg
     
  8. May 1, 2012 #7
    Ok.

    I can add forces in the same way??
     
  9. May 1, 2012 #8

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    what do you mean? :confused:
     
  10. May 1, 2012 #9
    Ok.

    I understand all, thanks you.

    I greet! :-)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Object and Friction on the object
Loading...