If that physical property is weight, you can use what is known as a load cell. [DegrawSt] uses four 50 kg load cells to create a bathroom scale using an Arduino.

DO NOT connect in any ways the main power supply that drive the LOAD to the arduino and transistor circuitry! Turn OFF the relay with delay You can use this code example to introduce a delay in your ...

Looks like low-end load cells might not be up to measuring the output on your high-power pneumatic tools, at least not repeatedly, but they ought to hold up to most electric drivers just fine. And ...