Basics
The fundamental idea of a bond graph is that power is transmitted between connected components by a combination of "effort" and "flow" (generalized effort & generalized flow). Refer to the table above for examples of effort and flow in different domains. If an engine is connected to a wheel through a shaft, the power is being transmitted in the rotational mechanical domain, meaning the effort and the flow are torque (τ) and angular velocity (ω) respectively. A word bond graph is a first step towards a bond graph, in which words define the components. As a word bond graph, this system would look like:
A half-arrow is used to provide a sign convention, so if the engine is doing work when τ and ω are positive, then the diagram would be drawn:
A full arrow is used to indicate a measurement, and are referred to as signal bonds, because the amount of power flowing through the bond is insignificant. However, it may be useful to certain physical components. For example, the power required to activate a relay is orders of magnitude smaller than the power through the relay itself; making it relevant only to convey whether the switch is on, not the power consumed by it.
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