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How does a doughnut-shaped object expand?

A tube from a car tire is free (no tire on it, no wheel within it) and it's inflated to a regular torroidal shape.

Say the diameter across the inside (the wheel diameter) is 50cm. If we inflate it further, will this distance increase, decrease, or remain the same?

The tube itself will become "fatter" but will this be compensated by its becoming longer?

1 Answer

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  • 7 years ago
    Favorite Answer

    A torus has two radii, and as these become closer

    to equal more "fattening" will result from inflation.

    As the radii diverge, more lengthening will result

    due to the distribution of stress over the surface

    compared with the volume.

    Maximizing volume to surface results in greatest

    fattening. Minimizing volume to surface favors

    rapid increase in major radius.

    For the proportions of an automobile inner tube

    I suspect both radii will increase, but the major radius

    will increase faster.

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