Mechanical Engineering

# DrD

Members

1,073

188

## File Comments posted by DrD

1. ### Turbosuper Chargers In Locomotives

379    2

Why is there a sudden change in spacing on p. 8 and again on p. 11? This makes for a strange looking document.

DrD

2. ### Kinematic Diagrams & Degrees of Freedom

609    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.

×
×
• Create New...