The idea of a physics calculator is to allow experimentation when physics equations are introduced.
Such a calculator would take inputs in a variety of units, and display the results of the calculation in different units.
One idea that is interested to me at least, is to allow a wide variety of interesting units, with contributed units. Newtons are a unit of force. So is a pound. But a 100HP car is another unit of force. The arm strength of a grown man is a possible unit. A unit of distance might be time to walk. A unit of weight may be a 10 year old boy. These units allow children to express (or read) values in meaningful ways, while also seeing a normalized form.
Someone put together something similar to this in Weird Converter.