kg/kWhour into litres/100m? is this possible, and if so how? what happens to the hour?
I would be more curious what happens to the kW and the meters.
Do you have a specific system in mind?
Or do you want to do the conversion by using physical constants (such as c and hbar), because then I think it is not possible (kg/kWh ~ s / m^2 while l/m ~ m^2).
What CompuChip is talking about is dimensional analysis. kg/kWh has dimensions of time2/length2, while liters/meter has dimensions of length2.
You can only convert from one form to another if both forms have the same dimensions. For example, you can convert from miles per hour to meters per second because both are in the form of length/time. There is no conversion from kg/kWh to liters/meter because the two forms are incommensurable.
D H explained my post very well. There are however two exceptions:
1) Physical constants are not mentioned; for example energy and mass have very different units (kg m^2 / s^2 and kg, respectively) although multiplying by the speed of light squared converts one into the other
2) There is some specific system which makes a conversion possible, for example: a water heater doing so-many kW of work will heat so many water by 1 degree (actually, this case looks a lot like 1, with the "missing" quantity being the specific heat of water which can convert Joules to degrees per kilogram, for example).
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