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SI units: slope vs. rate #4215

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on Oct 25, 2023

There are defined units indicating change of the unit over time. They have a suffix "slope" or "rate".

The question is:

Shouldn't this be unified?
Shall such units even be a part of Units.SI at all? See https://github.com/modelica/ModelicaStandardLibrary/pull/4103/files#r1152856158

Slope:

Modelica.Units.SI.CurrentSlope
Modelica.Units.SI.TemperatureSlope
Modelica.Units.SI.VoltageSlope

Rate:

Modelica.Units.SI.MassFlowRate
Modelica.Units.SI.VolumeFlowRate
Modelica.Units.SI.EntropyFlowRate
etc.

HansOlsson commented on Nov 1, 2023
HansOlsson
on Nov 1, 2023
Contributor
To me the first answer is 'No', and they are different even if the units are similar:

Slope indicates the derivative of a curve (w.r.t. time).

FlowRate indicates the rate at which the quantity flows past something (per unit of time). Thus a MassFlowRate doesn't necessarily indicate that the mass changes somewhere (especially not in a closed system), just that it flows past something (a valve etc).

With that line of thinking Current (not CurrentSlope) is a ChargeFlowRate.
So derivatives have slopes and connectors may contain flow-rates.
Reacted by tobolar
modelica
locked and limited conversation to collaborators on Nov 23, 2023
tobolar
converted this issue into a discussion #4236 on Nov 23, 2023
beutlich
added
wontfixIssue that will not be fixed
on Jan 9, 2024
beutlich
added this to the never milestone on Jan 9, 2024

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