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Mechanical Engineering

DrD

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  1. Overall, this is an interesting presentation. There is one significant problem that I see, however.

    In the discussion on the number of degrees of freedom a body has, it confuses the specific coordinates used to describe the configuration with the degrees of freedom themselves. The distinction is sometimes subtle, but it is important.

    Take a very simple example. Consider a point in a plane. How many degrees of freedom does the point have?

    We can describe the position completely by giving the cartesian coordinate of the point: (x,y).

    We can also describe the position completely by giving the polar coordinates of the point (r,theta).

    There are other possibilities (a bit more obscure), but the point is this:

    The point has 2DOF because in every case, two coordinates are sufficient to completely describe its position. The DOF are not x and y, nor are they r and theta. Degrees of freedom are not associated with specific coordinates, although we may choose to describe a degree of freedom by a particular choice of coordinate.

    This is a fine distinction, but it can be important.

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