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Thread: Quesion about Normal Force (Fn)

  1. #1 Quesion about Normal Force (Fn) 
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    Hi everyone!
    Question: Can a normal force cause an object to lift off a surface??

    Im guessing no because gravity is equal when it is stationary. However, there may be some other situations I can not think of.
    Any suggestions, or am i on the right path?
    Merci beaucoup in advance


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  3. #2  
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    N=Mg in most cases unless your on a surface that isn't parallel to the ground or there is some other force besides weight acting in the Y direction.

    If you go by that formulat then I don't see it as possible for normal force alone to lift a object off a surface. Normal force is just the reactionary force that conteracts the downward weight along with any other component of forces on the y axis.

    Does that explain it?


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  4. #3  
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    I think the Normal Force is explained well in the 3rd law of Newton.
    Every action has an equal and opposite reaction



    It isn't just the Y-axis or X-axis.
    It also occurs on surfaces with an angle.

    This force is perpendicular to the contact surface.

    On the question, the answer is no.
    It just balances the force placed on a surface.
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  5. #4  
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    "Normal" just means perpendicular to the surface. The normal component of gravity on a sloped surface would not generally cause it to lift off a surface (unless it were the bottom surface) but you could have a "normal" component of any force. So yes, I would say that a normal force could be away from the surface.
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  6. #5  
    Forum Senior anand_kapadia's Avatar
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    Normal force acts only when there is contact between two bodies. once you seperate the two bodies normal force vanishes.
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  7. #6  
    Forum Ph.D. Leszek Luchowski's Avatar
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    Quote Originally Posted by anand_kapadia
    Normal force acts only when there is contact between two bodies. once you seperate the two bodies normal force vanishes.
    I think you mean mechanical pressure. Which, if you look close enough, is the repulsion between the electrons in the atoms of the two bodies - so at the picoscale there is no such thing as "contact".

    But "normal" force means something completely different. Yes mechanical pressure can be normal to a surface (and actually must be if one of the bodies is a fluid at rest), but a lot of other forces can be normal to a surface.

    Gravity is approximately normal to the surface of the Earth, and it does work at a distance. So does electric and magnetic attraction and repulsion, which can also be normal to some surface.
    Leszek. Pronounced [LEH-sheck]. The wondering Slav.
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  8. #7 Re: Quesion about Normal Force (Fn) 
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    Quote Originally Posted by Jprojectrunway
    Hi everyone!
    Question: Can a normal force cause an object to lift off a surface??

    Im guessing no because gravity is equal when it is stationary. However, there may be some other situations I can not think of.
    Any suggestions, or am i on the right path?
    Merci beaucoup in advance
    All that "normal" means is "perpendicular". In order to lift a body away from a surface it is necessary to apply a normal force (normal directed away from the surface). So in fact in order to lift an object off a surface it is necessary to apply a force with a normal component.
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  9. #8 Re: Quesion about Normal Force (Fn) 
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    Quote Originally Posted by DrRocket

    All that "normal" means is "perpendicular". In order to lift a body away from a surface it is necessary to apply a normal force (normal directed away from the surface). So in fact in order to lift an object off a surface it is necessary to apply a force with a normal component.
    Normal does in fact mean perpendicular but in most physics classes it refers to the force that an object receives from another that it is causing a force onto. So you are not actually providing a normal force to lift an object but providing an applied force which could be in the form of a tension force for example.

    There is no way for the normal force to cause an object to lift off the ground but you can calculate if an object would leave the ground by finding out if the normal force is negative, which means there is not enough force keeping it on the ground.
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  10. #9 Re: Quesion about Normal Force (Fn) 
    Forum Ph.D. Leszek Luchowski's Avatar
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    Quote Originally Posted by HarryPotter
    Normal does in fact mean perpendicular but in most physics classes it refers to the force that an object receives from another that it is causing a force onto.
    What country do you live in, who is your minister of education, and when will he get his hard-earned beheading?
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  11. #10 Re: Quesion about Normal Force (Fn) 
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    Quote Originally Posted by Leszek Luchowski
    Quote Originally Posted by HarryPotter
    Normal does in fact mean perpendicular but in most physics classes it refers to the force that an object receives from another that it is causing a force onto.
    What country do you live in, who is your minister of education, and when will he get his hard-earned beheading?
    What do you mean by that? I was just referring to the question that was the beginning to this discussion. The person who wrote it is most likely taking a physics class so I was trying to help him out by saying the meaning that the physics book was most likely referring to.
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  12. #11 Re: Quesion about Normal Force (Fn) 
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    Quote Originally Posted by HarryPotter
    Quote Originally Posted by Leszek Luchowski
    What country do you live in, who is your minister of education, and when will he get his hard-earned beheading?
    What do you mean by that? I was just referring to the question that was the beginning to this discussion. The person who wrote it is most likely taking a physics class so I was trying to help him out by saying the meaning that the physics book was most likely referring to.
    I mean the physics book is wrong if it uses the word normal to mean reaction. It's just as if a chemistry book used the word copper to mean mercury. Crazy.

    I understand your reply was right under the circumstances, just like "don't use the elevator" is right during a fire. It's the circumstances I find abnormal.
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  13. #12  
    Forum Senior anand_kapadia's Avatar
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    hey normal force acts during collision of a ball, when falls on a surface.
    The impact force which acts is actually normal force...........
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  14. #13 Re: Quesion about Normal Force (Fn) 
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    Quote Originally Posted by HarryPotter
    Quote Originally Posted by DrRocket

    All that "normal" means is "perpendicular". In order to lift a body away from a surface it is necessary to apply a normal force (normal directed away from the surface). So in fact in order to lift an object off a surface it is necessary to apply a force with a normal component.
    Normal does in fact mean perpendicular but in most physics classes it refers to the force that an object receives from another that it is causing a force onto. So you are not actually providing a normal force to lift an object but providing an applied force which could be in the form of a tension force for example.

    There is no way for the normal force to cause an object to lift off the ground but you can calculate if an object would leave the ground by finding out if the normal force is negative, which means there is not enough force keeping it on the ground.
    I don't know where you learned your physics, but in all cases with which I am familiar "normal" is perpendicular. Period. What is the case is that forces between bodies in contact are often taken as normal to the surface of each, except for frictional forces that are in the plane of both surfaces. If you want to separate two bodies it is the normal component of the force that causes the separation. If, for instance you want to cause a spring to jump off of a surface, you first apply a compressional normal force, then release the spring which results in a rebounding momentum that is also normal to the contact surface.

    What is true is that a normal force directed towards the plane of contact will not cause two bodies to separate, which is nothing more profound than noting that in a free body diagram the forces are all either parallel or tending to compress the two bodies together. But to separate them you MUST appy a force with a normal component and it is that component, in the proper direction, that causes the separation.
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