So we know how they work ?
The theory of gravity is an explanation of how things fall.not the action but the attempt to explain the cause of gravity.magnetism isn't connected to gravity.our moon has gravity but no poles of magnetic energy.
With electricity,we can use it but what moves isn't so simple.no there's is no such thing as a positive particle moving.only electron,quark will move .
There is a debate on how it moves called hole theory ,one electron moves in another moves out looking for that balence.
Theories which we use to make things work.
We knew about gravity ,newton theorized how gravity worked from his observation of the planets abd we have calculus,and orbital planes from his work.
https://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation
Supreceded by laws of relativity.
I'm a creationist but let's not assume that an observed phenomon of gravity is understood.it's not .in conclusion, these theories are explanations of natural phenomenon that can be tested.
Germ theory, atomic theory, the above named ones,all are things we see or can observe and try to explain how it works.
Gravity is observed but not fully explains yet,we can sling shot probes way out using known theories.