In the model above, the output will be 2 regardless of whether the switch is open or closed. This is caused by the fact that the switch is not actually completely open; rather, it still has some impedance that is specified by the open conductance in the block’s dialog.
To get behavior that is more indicative of the switch utility, you could use a switch to open or close a short circuit. The following model demonstrates how the switch can be used, and the circuit that it represents:
As illustrated in the screenshot above, the models on the left use a switch (threshold 3), while those on the right use resistors with resistances set to match the resistance/conductance specified for closed and open circuit values of the corresponding switch. In the top models, the switch is open -- represented on the left by a very high resistance. In the bottom case, the switch is closed, as represented on the right by a very low resistance. In both cases, the resistances on the right match those specified in the corresponding Switch Block parameters.
Depending on the specific application, the PS Switch block may be closer to what you are trying to model. Additionally, you may find more information on the switch block in the documentation: http://www.mathworks.com/help/physmod/simscape/ref/switch.html.
