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Inertia and momentum

  1. Nov 22, 2006 #1
    Are they the same thing?
    momentum = p = mv
     
  2. jcsd
  3. Nov 22, 2006 #2
    Inertia is more like m
     
  4. Nov 22, 2006 #3
    Interia has no numerical value unlike momentum. It's just a property of an object based on its mass.
     
  5. Nov 23, 2006 #4
    Ok, that's what I thought. But then, how would you define momentum? (in words)
     
  6. Nov 23, 2006 #5
    "momentum is the measure of inertia "
    and inertia is the property of the system or the object to resist a change in its state i.e either the state of motion or of rest
     
  7. Nov 23, 2006 #6
    Inertia is unchanging whereas momentum can be changing. (for all classical approx.)

    momentum is concerned with moving things.
     
  8. Nov 23, 2006 #7

    russ_watters

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    Staff: Mentor

    Inertia is related to mass. Momentum is related to mass and speed (as the equation shows).
     
  9. Nov 23, 2006 #8
    Virtual said momentum is the measure of inertia.
    Then, velocity must be part of inertia. I think it makes sense since the faster the object is going, the harder it is to change its condition...am I right?
     
  10. Nov 23, 2006 #9
    I wouldn't equate inertia with momentum. It's just as hard to stop a fast object as it is, after stopping it, to then speed the object back up again, however the stationary object has infinitely less momentum.

    Perhaps a formal definition for inertia (or moment of inertia) should be the force (or torque) with which an object resists a change in its velocity (or in its angular velocity). Consequently, the SI unit for inertia would be kg (or, er, kgm^2/rad).
     
  11. Nov 23, 2006 #10

    russ_watters

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    Staff: Mentor

    Virtual was wrong to say that because....
    No, you are clearly not right as f=ma doesn't say anything about velocity, does it? If it got harder to change velocity when speed was higher, those terms should appear in that equation.

    (caveat: relativity not needed here)
     
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