A mechanical analogy to resistive vs reactive loads

[k4kyv]

This occurred to me the other day, while I was doing some emergency repairs after our recent windstorm, and was attempting to nail back some pieces of siding that had blown off.

Whenever I attempted to drive a nail through sheathing directly over a stud, the nail went firmly and soundly into the wood, with little effort.  But between the studs, the sheathing is springy and has "give" to it, and most of the energy from the hammer blows tends to momentarily displace the wood instead of driving the nail.  The wood reflects the energy back to the hammer and it bounces.  Often I end up bending the nail and/or splitting the wood, mashing my finger, and usually cussing a lot.

It occurred to me that nailing directly over solid studs is analogous to working a feedline into a purely resistive load.  The energy exerted by the hammer simply overcomes the resistance of the wood to the nail, and the nail is forced into the wood, with little reaction or bounce.

But over the springy part, the sheathing "reacts" to the blows of the hammer, and "reflects" most of the momentum back to the carpenter.  The nail goes slightly deeper into the wood, but most of the energy is reflected back to the sender.  If enough energy is reflected back it can cause injury.

This is exactly what happens when a flat feedline is terminated into a purely resistive load.  There is no energy reflected back; it all goes to heat up the resistance or radiate into space.  But to a highly reactive load, most of the energy is reflected back and only a portion goes into the load.  Weird things may happen if the system is not properly tuned to resonance to cancel out the reactance, such as capacitors flashing over and coils heating up  due to high circulating currents.  Again, it may cause me to cuss a lot.

[WA1GFZ]

I love to stand outside the back door and twang the 90 foot clothesline watching the standing wave travel back at me.