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Homework Help: Normal Force Definition

  1. Feb 10, 2012 #1
    Which is true/false? When a force is called a "normal force", it is:

    A force that is always equal to the weight of the object.

    A force that is perpendicular to the surface of the Earth at any given location.

    A contact force perpendicular to the contact surface between two solid objects.

    The net force acting on the system.

    A force that is always vertical.

    I answered: true, true, not sure, not sure, true(?).
    Last edited: Feb 10, 2012
  2. jcsd
  3. Feb 10, 2012 #2


    Staff: Mentor

    Why not look up the definition of normal force? And answer based on that.
  4. Feb 10, 2012 #3
    A contact force perpendicular to the contact surface between two 'solid' objects.

    only this one is correct!
    however, 'solid' is a funny way to describe this. You would then need to define a solid, which is chemistry based, however, it does make sense to add 'solid' into the statement, because then the force of contact between to objects that are not 'solid' redefines the friction dynamics of these forms of contact. Only a Normal force can create kinetic or static friction. Other than that, the friction would be considered 'drag' force or 'viscous' force, etc. You understand what I'm saying?
  5. Feb 10, 2012 #4
    "I answered: true, true, not sure, not sure, true(?)."

    For your first answer, think about how the normal force can change on an incline plane. Do you know what that looks like?

    For your second answer, also think about how the normal force vector directs on an incline plane.

    For your third answer, refer to what I talked about on the previous comment.

    For your fourth answer, a net force describes the force of effect. You see what I mean? When there is a cause (a force) then the effect is (net force), which is defined as the sum of the forces. Therefore, a normal force is only an element of the net force. They are not the same.

    For the fifth answer, think about what vertical means and how the vector of the normal force can change.
  6. Feb 11, 2012 #5
    All right, thank you for all your help!
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