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Homework Help: Always centripetal force when object in circular motion?

  1. Jan 25, 2006 #1
    Centripetal force is directed towards the circle, but is centripetal force always involved when objects go in circle?If I put a toy car on ice and drive it around in circle with my hand, then obviously force my hand exerted was directed along the path(circle) and not towards center of circle.

    So if in this case force wasn't directed towards the center, wouldn't that say that centripetal force is not always needed for things to have circular motion?

  2. jcsd
  3. Jan 25, 2006 #2
    According to the First Newton Law of Motion, a resultant force must act if there is a change of direction. In circular motion, the object always change direction----hence it is a must to have a centripetal force acting on it.

    As for your case, i think(I'm not sure though) that the centripetal force is acting on your hand.
  4. Jan 26, 2006 #3
    Why? Why couldn't resultant force directed along tha path also made object go in circles? Why would only centripetal force cause such motion?
  5. Jan 26, 2006 #4
    You have to remember that any force acting on a partical that travels non-linearly has two distinct components. One acting tangential to motion, the other acting normal to the motion. If there is no normal force, the partical's motion will be linear only.
  6. Jan 26, 2006 #5
    I didn't say there was no normal force.But since besides normal component there is also component of force tangential to motion the resultant force isn't directed towards center of circle.
  7. Jan 26, 2006 #6
    No, but the resultant force has a normal component.
  8. Jan 26, 2006 #7
    I don't know what you are trying to say!

    I'm also not quite certain why component of force needs to be tangent to motion?
  9. Jan 26, 2006 #8
    The particle do accelerate if it is not travelling linearly. You may use a vector diagram to figure it out. If there's acceleration, there should be force acting on the particle. In circular motion case, the centripetal acceleration acts towards the center, so the centripetal force must occur.
  10. Jan 26, 2006 #9
    They don't have to be tangential or normal. You can use any system you want to show the forces.

    But we like to break up any force acting on a body in curvilinear motion INTO T & N components.
  11. Jan 27, 2006 #10
    I think I do understand why component of force needs to be tangent to motion. Because it can only change magnitude of velocity if it's parallel to velocity and since velocity is tangent to motion so must be component of force.

    But even in this scenario where one component is perpendicular and other parallel to velocity, resultant force is not directed towards the center of circle. So this can't be centripetal force and yet object si going in circular motion!
  12. Jan 29, 2006 #11
    I hope I'm not breaking any rules by doing this, but can't you guys help me some more? The stuff I asked about are basics, all of physics I have yet to learn is built up on this.:cry:
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