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Physics Questions / Tips

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    #32
    cocoa
    Registered Users Posts: 1,269 ✭✭✭cocoa


    microbiek wrote:
    T^2 is proportional to R^3

    O_o, calling it "kepler's law" is a bit of stretch, considering there was three laws, and they referred to eliptical orbits, not just circular ones, and you derive a formula, not just that proportion, and nowhere in the syllabus do they call it kepler's law...


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    #33
    microbiek
    Closed Accounts Posts: 93 ✭✭microbiek


    cocoa wrote:
    O_o, calling it "kepler's law" is a bit of stretch, considering there was three laws, and they referred to eliptical orbits, not just circular ones, and you derive a formula, not just that proportion, and nowhere in the syllabus do they call it kepler's law...



    ive seen it they do call it that and its sumtin lik T^2=GMm/R^3(4pi^2) is the formula nt sure!!


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    #34
    cocoa
    Registered Users Posts: 1,269 ✭✭✭cocoa


    microbiek wrote:
    ive seen it they do call it that and its sumtin lik T^2=GMm/R^3(4pi^2) is the formula nt sure!!
    have a look at fobia's link to the syllabus, nowhere is the word "kepler" in it. You haven't got the formula right, but I think you're thinking of the right thing. Kepler's third law mentions the proportion between T^2 and R^3, not the formula...


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    #35
    Nehpets
    Closed Accounts Posts: 1,504 ✭✭✭Nehpets


    Feddd wrote:
    When the exam is being made out, the short questions are done last (Q5). They are the things that "Didn't get a go" that year and are likley to come up the next year in long Qs.

    Where did you get that info?


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    #36
    carlowboy
    Registered Users Posts: 1,152 ✭✭✭carlowboy


    That's not one of Kepler's laws though. What exactly is it called?


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    #37
    cocoa
    Registered Users Posts: 1,269 ✭✭✭cocoa


    carlowboy wrote:
    That's not one of Kepler's laws though. What exactly is it called?
    it is, technically, a very special case of the third law. It's not given a special name in the syllabus, I don't know if it has one, I've always just called it "formula for the period of a satelite (in a circular orbit)"


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    #38
    microbiek
    Closed Accounts Posts: 93 ✭✭microbiek


    cocoa wrote:
    have a look at fobia's link to the syllabus, nowhere is the word "kepler" in it. You haven't got the formula right, but I think you're thinking of the right thing. Kepler's third law mentions the proportion between T^2 and R^3, not the formula...

    oh ryt yeah its T62=4pi62R^3/GM you derive it by saying newtons grav equals centripetal force ye its just pat doyle goin into extar detils just sayin that it states t^2 is prop to R^3


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    #39
    microbiek
    Closed Accounts Posts: 93 ✭✭microbiek


    motion of a satellite: The moon is a satellite of the earth Keplers 3rd law states that the periodic time squared is proportional to the radius cubed


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    #40
    Tomlowe
    Closed Accounts Posts: 131 ✭✭Tomlowe


    it's keplers third law and its derivation has come up before.


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    #41
    microbiek
    Closed Accounts Posts: 93 ✭✭microbiek


    Tomlowe wrote:
    it's keplers third law and its derivation has come up before.

    came up in the mocks


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    #42
    carlowboy
    Registered Users Posts: 1,152 ✭✭✭carlowboy


    Tomlowe wrote:
    it's keplers third law and its derivation has come up before.


    They didn't word it as Kepler's law in the question though did they?


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    #43
    cocoa
    Registered Users Posts: 1,269 ✭✭✭cocoa


    Tomlowe wrote:
    it's keplers third law and its derivation has come up before.
    no, it's a formula which happens to be very special case of kepler's third law. You don't have to know the law, or have any extra knowledge about the proportion which happens to be contained in the formula.


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    #44
    microbiek
    Closed Accounts Posts: 93 ✭✭microbiek


    where can you get all the syllabuses paticularly the engineering one???


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    #45
    microbiek
    Closed Accounts Posts: 93 ✭✭microbiek


    cocoa wrote:
    no, it's a formula which happens to be very special case of kepler's third law. You don't have to know the law, or have any extra knowledge about the proportion which happens to be contained in the formula.


    it just works out that way when you let w=2pi/T


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    #46
    carlowboy
    Registered Users Posts: 1,152 ✭✭✭carlowboy


    cocoa wrote:
    no, it's a formula which happens to be very special case of kepler's third law. You don't have to know the law, or have any extra knowledge about the proportion which happens to be contained in the formula.


    Well its not a very special case. It deals with circular orbits not eliptical ones (which Kepler's 3rd law was about). But most planet's orbit and satellites orbit are very close to circular so it is reasonably argument. Its not relevant at all in comets though.

    You're right though.


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    #47
    cocoa
    Registered Users Posts: 1,269 ✭✭✭cocoa


    there's no w in that formula, you don't have to study the link between simple harmonic motion and circular motion. There's no "working out" necessary, the formula is an equation, as it happens everything other than R and T are constant, so they are proportional, simple, but totally unnecessary for the LC course.

    syllabuses


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    #48
    microbiek
    Closed Accounts Posts: 93 ✭✭microbiek


    cocoa wrote:
    there's no w in that formula, you don't have to study the link between simple harmonic motion and circular motion.

    syllabuses


    ther is at the start as centripetal f = mw^2R its not w its a greek letter........thanks for the syllabuses


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    #49
    cocoa
    Registered Users Posts: 1,269 ✭✭✭cocoa


    microbiek wrote:
    ther is at the start as centripetal f = mw^2R its not w its a greek letter........thanks for the syllabuses
    oh, you mean omega, angular velocity. It's still not in the formula for the period of a satelite, you mean the derivation? I suppose if you do let omega equal that then it works out that R^3 and T^2 are equal, but that's really beside the point...


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    #50
    JC 2K3
    Closed Accounts Posts: 7,794 ✭✭✭JC 2K3


    cocoa wrote:
    there's no w in that formula, you don't have to study the link between simple harmonic motion and circular motion. There's no "working out" necessary, the formula is an equation, as it happens everything other than R and T are constant, so they are proportional, simple, but totally unnecessary for the LC course.

    syllabuses
    syllabi.


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    #51
    carlowboy
    Registered Users Posts: 1,152 ✭✭✭carlowboy


    JC 2K3 wrote:
    syllabi.

    Thought I'd come across as a pedantic git if I said that :D


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    #52
    cocoa
    Registered Users Posts: 1,269 ✭✭✭cocoa


    JC 2K3 wrote:
    syllabi.
    maybe, maybe not. I've never seen five bi, or omnibi go past my stop... :P


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    #53
    eZe^
    Registered Users Posts: 7,046 ✭✭✭eZe^


    Syllabuses is perfectly accepted too.


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    #54
    JC 2K3
    Closed Accounts Posts: 7,794 ✭✭✭JC 2K3


    I haven't seen many stadiums either.


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    #55
    cocoa
    Registered Users Posts: 1,269 ✭✭✭cocoa


    *pumps fist*

    whoah, off-topic -ness FTL... :(


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    #56
    JC 2K3
    Closed Accounts Posts: 7,794 ✭✭✭JC 2K3


    pfft, stupid perfectly acceptableness.

    Why omit a Latin suffix if you have the option?

    Ommitting Latin suffici ftl.


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    #57
    eZe^
    Registered Users Posts: 7,046 ✭✭✭eZe^


    Anyway, anybody a bit too lazy to study the ole physics. Its like I know most of it already but I really need to refresh everything but I cba to look through all the stuff I know just to find the valuable things!! :D Same with chemistry... oh god.


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    #58
    carlowboy
    Registered Users Posts: 1,152 ✭✭✭carlowboy


    I study physics because it gets me away from studying for Economics :D


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    #59
    eZe^
    Registered Users Posts: 7,046 ✭✭✭eZe^


    carlowboy wrote:
    I study physics because it gets me away from studying for Economics :D


    I love physics, but I went over electricity today, and the only real things I needed to refresh were the wheatstone bridge, resistivity and capacitance, I basically wasted 2 hours trudging through a load of crap! :D


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    #60
    carlowboy
    Registered Users Posts: 1,152 ✭✭✭carlowboy


    Only was to study right now imo is going through the exam papers, questions in Edco's experiment book and sample papers.


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    #61
    Tomlowe
    Closed Accounts Posts: 131 ✭✭Tomlowe


    JC 2K3 wrote:
    Ommitting

    omitting.
    JC 2K3 wrote:
    suffici

    suffices.


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