What is exact connection between Simscape model and original physical system? Does simscape elements take direction in space?

For example in the image taken from "http://de.mathworks.com/help/pdf_doc/physmod/simscape/simscape_lang.pdf" page 2-21. I have attached the image, please take look at it. Que1: Does reference.ssc have direction? now its vertical in image, if I rotate it by 90 degree, will it represent horizontal reference in real physical system? If not what needs to be done? Que2: Does connecting lines between various elements have dimension? I mean length? If it is not, then how can we account for separation between two elements? for example spring and dash pot. Que3: When we connect a mass to system what exactly happens? I mean is it like we connect a point mass to system or whole system takes that mass? or something else is happening? Precise and brief answer is expected. If you know documentation explaining these things please do share in the answer. Thank you in advance :) </matlabcentral/answers/uploaded_files/36832/Screenshot%20from%202015-09-10%2012:01:17.png>

Answer 1

[Sebastian Castro]

Q1:

Rotating the reference blocks does not have any effect on the directionality of the model -- it is purely visual. All Simscape reference blocks have one purpose; that is, to define the Across variable (e.g. Voltage, Velocity, Pressure, etc.) as zero at that point.

Q2:

The mechanical domains in Simscape use the variables of Velocity and Force/Torque. All position values are determined by integrating the velocity from some initial condition. This is somewhat related to your previous question about building a spring using the Simscape language.

As another example, you can look at the Ideal Translational/Rotational Motion Sensor blocks. Those blocks also require you to enter an initial condition for the displacement, so the velocity can be integrated from that starting value.

Q3:

When you connect a mass to the system you are adding another possible "flow path" for the force running through the system at that node. Whatever force flows into, or out of, the Mass block affects how that mass accelerates.

F == m*a

This creates the relationship between the conjugate variables in the Simscape mechanical domain: Force and Velocity.

F == m*v.der

- Sebastian