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Thread: Question about newtons laws

  1. #1 Question about newtons laws 
    Forum Freshman
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    Alright so weve done a prac in school which is based around Newtons Second Law.

    I was typing up the results/analysis for a prac report and saw a relation between the acceleration, mass and distance the object travelled as.

    a=d/m

    Where:

    a=acceleration (ms-2) ( the -2 ment to be superscirpt but i don't know how to do iton a html page)

    d=distance travelled (in this case a constant of 1m)

    m=the objects mass in kilograms

    Any way so i'm trying to figure out if this is right or not, the original equaiton was:

    a=1/m

    and since we were always measuring 1m as a constant i assumed that the 1 was distance travelled.

    I think this has some sort of a relation to Newton's Second Law where a=F/m but i'm honestly not sure.

    Very confused please help.


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  3. #2 Re: Question about newtons laws 
    Forum Ph.D. Leszek Luchowski's Avatar
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    Quote Originally Posted by mathew0135
    ...saw a relation between the acceleration, mass and distance the object travelled as.

    a=d/m

    Where:

    a=acceleration (ms-2) ( the -2 ment to be superscirpt but i don't know how to do iton a html page)

    d=distance travelled (in this case a constant of 1m)

    m=the objects mass in kilograms
    No wonder you are confused, this "relation" makes no sense. If the source that gave it to you was a human, distrust him (or her, or them); if a book, recycle it.

    Why on earth would acceleration equal distance divided by mass?

    Please tell us what you are trying to do/learn/understand, and I'm sure you can find help here.


    Leszek. Pronounced [LEH-sheck]. The wondering Slav.
    History teaches us that we don't learn from history.
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  4. #3 Re: Question about newtons laws 
    Forum Professor sunshinewarrior's Avatar
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    Quote Originally Posted by mathew0135
    Any way so i'm trying to figure out if this is right or not, the original equaiton was:

    a=1/m

    and since we were always measuring 1m as a constant i assumed that the 1 was distance travelled.

    I think this has some sort of a relation to Newton's Second Law where a=F/m but i'm honestly not sure.

    Very confused please help.
    If the equation you were given was:

    a = 1/m

    then it wasn't an equation, but an expression of the inverse relationship between acceleration and mass - the greater the mass, for a given force, the less the acceleration.

    The 1 therefore, in your original equation just signifies a reciprocal, not a metre.

    If it was you who made the assumption that the 1 referred to a metre, then you have now learned how assumptions (and even leaps of cognition!) can frequently lead us astray.

    If, however, the 'equation'

    a = d/m

    was given to you by someone, then yes, as Laszek said, cease to trust that person's ability to not make mistakes in mechanics! :P

    Perhaps a simpler way to explain how your original relation works it to state it as:

    a = cm<sup>-1</sup>

    Where 'c' represents some constant that needs to go into this equation based upon the original context.

    Does this help clarify?
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  5. #4 Re: Question about newtons laws 
    . DrRocket's Avatar
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    Quote Originally Posted by mathew0135
    Alright so weve done a prac in school which is based around Newtons Second Law.

    I was typing up the results/analysis for a prac report and saw a relation between the acceleration, mass and distance the object travelled as.

    a=d/m

    Where:

    a=acceleration (ms-2) ( the -2 ment to be superscirpt but i don't know how to do iton a html page)

    d=distance travelled (in this case a constant of 1m)

    m=the objects mass in kilograms

    Any way so i'm trying to figure out if this is right or not, the original equaiton was:

    a=1/m

    and since we were always measuring 1m as a constant i assumed that the 1 was distance travelled.

    I think this has some sort of a relation to Newton's Second Law where a=F/m but i'm honestly not sure.

    Very confused please help.
    You appear to have given only a portin of the problem statement. Based on what you have provided there are a couple of possibilities:

    1) Someone has completely scrambled Newton's second law, which is F=ma in the case of constant m. You have correctly stated this law in your last sentence.

    2) You have a situation in which force F is proportinal to distance. This is the case with a simple linearly elastic spring.

    In any case the question of whether your equation, a=1//m is right or not is dependent on the physical situation, which you have not specified. It is not an expression of general applicability. The question is one of physics and not one of mathematics. A proper answer requires a description of the physics involved.
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