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  • physics help?
  • bikerbruce
    Free Member

    if the sun has a diameter roughly 100x that of the earth, how many times greater is the volume of the sun than that of the earth?

    mrmo
    Free Member

    i am not going to tell you the answer just what you need to know, pi,

    calculate the volume of one based on the diameter x then calculate the volume of the other based on a diameter of 100x.

    you should be able to get the answer quite simply from that

    brakes
    Free Member

    million
    .
    pi is irrelevant mrmo

    bikewhisperer
    Free Member

    i am not going to tell you the answer just what you need to know, pi

    fail.

    j_me
    Free Member

    basic geometry

    IanMunro
    Free Member

    For a given scaling factor n
    Lengths increase by n
    Areas by n^2
    Volumes by n^3

    mrmo
    Free Member

    i am not going to tell you the answer just what you need to know, pi

    fail.

    It may be irrelevant to the answer but if you actually bother to find out the correct equations to get the volume, which use pi, then actually use your head to get to the answer it is a very easy question to answer. How do you learn but by doing?

    j_me
    Free Member

    fail^2

    IanMunro
    Free Member

    🙂

    Flaperon
    Full Member

    Another way to look at it. Consider it from a dimension point of view (this works just as well with a cube as with a sphere, pi doesn’t come into it).

    1-D: If the sun and the earth are one dimensional objects, then the sun is 100x bigger than the earth.

    2-D: Imagine the earth is a square of length 1. If we make it 100x larger, then it grows in length and width. 100 x 100 = 10,000 times more surface area. (100 squared)

    3-D: Your example. Our square is now a cube of length 1 on all sides. Let’s make it 100x bigger. It grows by 100 on the length, width, and depth. 100 x 100 x 100 = 1,000,000 times heavier (100 cubed).

    Think of it in terms of one-unit blocks if you want. Bakes has the simple answer. 🙂

    I learnt this maxim at school, in terms of how volume (or mass) increases with factors in terms of throwing things down a 1000ft mine shaft.

    * A mouse is unharmed.
    * A rat is stunned.
    * A man breaks.
    * A horse splashes.

    bikerbruce
    Free Member

    sorry dont even do physics its for my girlfriend…

    toys19
    Free Member

    what they are trying to tell you is that the volume is proportional to the radius cubed (radius x radius x radius) so 100 x 100 x 100 = 1000000.
    And there is your answer.

    LoveTubs
    Free Member

    If you need help, PM me…that’s if this site supports PM’s….erm ❓

    simonfbarnes
    Free Member

    you don’t need pi to get the answer 🙂

    and it’s geometry, not physics…

    bikerbruce
    Free Member

    i just need to know that then i’ll be in her good books

    Cougar
    Full Member

    Volume of a sphere is 4/3 pi r^3

    to compare two, most that cancels out – it’s basically the cube of the radius.

    So if the Sun’s diameter is 100x the Earth’s, it’s 50x the radius, so 50^3 times the volume, or 125,000 times larger.

    Cougar
    Full Member

    As an aside, the volume of a cylinder is the area of a circle (pi r^2) multiplied by its height.

    So to calculate the volume of a pizza of height ‘a’ and radius ‘z’, the volume is pi.z.z.a

    Hai thengyoo.

    bikewhisperer
    Free Member

    So if the Sun’s diameter is 100x the Earth’s, it’s 50x the radius, so 50^3 times the volume, or 125,000 times larger.

    That makes the Sun’s radius 50x the diameter of the earth or 100x the radius.. so still 100^3

    mrmo
    Free Member

    Cougar no, the idea is right, but the diameter is always 2 x the radius. So if the diameter is 100 times greater the radius is also 100 times greater.

    simonfbarnes
    Free Member

    So if the Sun’s diameter is 100x the Earth’s, it’s 50x the radius, so 50^3 times the volume, or 125,000 times larger.

    nearly right, except the ratio of the diameters is the same as the ratio of the radii 🙂

    deadlydarcy
    Free Member

    No, it’ll still be 100 times the radius. It all cancels out. All you’re left with is the factor.

    j_me
    Free Member

    yep – fail^3

    brakes
    Free Member

    what do I win?

    bikerbruce
    Free Member

    THANKS GUYS….IM GONA GET SOME…

    duntstick
    Free Member

    Any wiser? 😀

    bikewhisperer
    Free Member

    what do I win?

    a million!

    Cougar
    Full Member

    Ah, nads, I used to know this stuff; more haste, less speed.

    On a point of pedantry, the original premise is wrong. It’s closer to 109 times larger. That gives an outcome of ~ 1,295,000 times larger, which is why 125000 looked right and 1000000 didn’t.

    simonfbarnes
    Free Member

    On a point of pedantry, the original premise is wrong. It’s closer to 109 times larger

    that’s it, blame someone else for your mistake 🙂

    the OP says “roughly”, but of course naming the sun and the earth is irrelevant to the problem

    CharlieMungus
    Free Member

    I guess that’s why they prefaced it with ‘if’

    Cougar
    Full Member

    Oh give over. :-p I wasn’t blaming anyone for my own carelessness, just trying to provide a value-added service. Or something.

    j_me
    Free Member

    Of course the premise is wrong, as neither the earth nor the sun are perfectly spherical 🙂

    LoveTubs
    Free Member

    This thread is turning out to be a) highly amusing and b) worrisome 😯

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