What is the best program for electrical and engineering prototyping?

I am searching for a program that does simulations of electrical or engineering components put together. Let's say you start with a simple kit of parts like a set of pistons, spark and fuel supply or a preset electrical coil motor and fan blades and then press "START" and see a simulation of what happens when all the physical forces start interacting. I would really love to know which programs are out there - from the intuitive and interactive to the more advanced with a dual 2D CAD and 3D design capability, with circuitry diagrams and the whole package. If you need a simple example let's say I want to create a source of water flowing, along it I place a turbine connected to a coil motor connected to a battery and a lightbulb to go "on". All these componnects I expect to be standard tools of the software with preset resistance, power requirements, force, etc. As well as options to easily (or in detail with more effort) to create custom components and their physical attributes. Thank you guys - I like crocodile clips, looks very promising. Electronics workbench is great for circuitry. However, is there anything more advanced even, that you could take to the CAD/CAM machine to start producing the product? With same simulations capabilities? Like Pro-Engineer with Electronics workbench and Crocodile Physics & Technology combined. Many thanks in advance!!!