In a fluid system, it is the lag in any response to changes in the forces. It can be defined as the reaction to changes that depend on reactions to change. …
This sort of thing is an everyday occurrence you might be so familiar with that you pay it no attention.
You have a box of pins and take one out. Then you put the box away near a live electric circuit. Next time you need a pin the pins are clingy.
What has happened is that the steel in them has become magnetised. It takes a fraction of a second longer to select a pin. Who would pay any attention to that?
You leave an house unattended for a few days. The next time you come back the taps don't pour straight away. The water has drained or gas pressure has bubbled out of the system and flows through the line.
Before the tap was an on off switch now it is part of a fluid system that has latency.
You are probably familiar the physics of latency from your days in school. And never thought about how it concerns you since. Well, if it costs 10 quid to boil water from zero it is going to cost another 8 quid to raise it to steam.
Not a major problem for most householders where "hot" water isn't all that many degrees above ambient temeperatures.
But you electricity supplier needs to know what the temperatures are so he can give you a competitive bill. The company needs to know how much it will cost to convert the steam from atmospheric pressure to something they can use in the turbines.
Something that doesn't concern you. I admit I never think about it either. Not even when it directly concerns the way my fridge and freezer works. I never paid any attention to how much it costs to convert the warm food into frozen food or what temperatures the CFC oils work at. I just want to know it doesn't need de-icing too often and won't break down.
And if it smells so bad I aught to think about cleaning it one day.
But hysteresis works in the national economy too. In ways that may well have a devastating effect on you. Think about all the houses up for sale near you. They won't sell because nobody has any money to buy or reason to move. That's hysteresis.
Well not the full story but you can make a system simple or complex. I may come back to this point.
In the good times people move to get a bigger or better house. This leaves a vacancy for someone moving into an area for a new job or for someone who has work and just got married.
Out of work locals take up any jobs going, out of work people don't get married. People don't have families, people don't move up the chain. The chain of house buyers is a fluid system. It depends on all aspects of it working unit by unit in a pattern that we know has worked for decades.
Suppose air pressure increased and decreased by much greater margins, world wide, seasonally. It would be more difficult to boil water sometimes until the pressure drops. No big problem in real life, as changes likely to occur are minor. But suppose it was a big event and you never knew from day to day which it was going to be.
Suppose rainy weather has very low pressure below what is rare in Britain 28 inches (950 mb) and it rarely stays that low for more than a day or two. It never gets much higher than 31 inches (1050 mb) either.
But suppose it went much further than those extremes and stayed there for weeks at a time, with each passing Low and High pressure systems lasting the whole spell or two instead of just peaking at that extreme one day in seven.
If the pressure drops to 900 mb every time it dropped and stayed there for the run of the weather and then it rose with fine weather to 1100 mb. That would affect your electricity bill noticeably.
How often do you suppose you'd think about changing your supplier?
But other things happen to the system to make it more confusing. Power stations have a lot of fuel in stock, with options to buy more at a price agreed ages ago. But there may be a problem in delivery. The price amy go up anyway, with taxes or unforseen circumstances.
These days electricity companies can tell what programmes running on TV will require more electricity when and why.
A big sports match will bring a massive jump in consumption half way through as people make hot drinks and switch on cookers. They can even meter what time the commercials come on in soap operas. These things are now part of the system and play a big part in future contracts to both customers and fuel suppliers alike.
Hot weather causes less heat to be used to provide water for bathing but people bath more often. And require more power for coolers. When electricity was first put in by large utilities, they didn't know about these things and had to over supply. Because in those days winding up coal fired furnaces took hours and they had to keep extra on tap to allow for full use, knowing a lot was going to go up in smoke wasted.
If they tried to second guess they would be introducing a latency into the system that customers would complain about. That would be a level of hysteresis.
Today it is all catered for. They know when people will be sitting outside or off visiting rather than staying home watching TV.
Similar techniques are used by your ISP to monitor your use of their service. Sometimes it is to know what sort of hardware to invest in next. Server contracts with IBM and Cisco etc cost most of their budget after the phone and electricity bills.
Sometimes they want to block your access to certain channels that may or may not be popular pirate sites.
Firms that sell adverising want to know what sort of things you look at online. And governments want to know what you are thinking and doing about it. That may be for the good of mankind when it cracks down on depravity and may be a bad thing when they want to round up people who might cause trouble for the regime.
It's no secret that the NSA was doing all sorts of dirty things for the chimpanzee and as far as I know is still doing it for the present government in the USA. In fact it would take the new presidency some time to regain control of that system. They have to work out exactly what was going on and what would be best done about it. Latency in the system. Hysteresis.
I have no doubt at all that in Britain where we have no protection from eaves-dropping this sort of thing has been going on since the 1970's or earlier.
Well now you kow a little bit about histeresis. Much good may it do you.
About the housing chain.
When the economy picks up there will be evenmore histeresis in the system as people need to reconsider their positions when they want to move up or down the chain..
Hoses in relativley good positions now will be in poor ones maybe when factories close and do not reopen. People will wnat to move to the new places that the factory jobs are further depressing some area and making others boom towns.
When people don't have money they neglect payiing for repairs and the desirablity drops. Gardens get neglected, families fall apart and foreclosures force people to leave anyway and houses fall into decay.
All sorts of things happen to a system that has a sudden change forced on it. You may be familiar with an old vehicle that has been parked unused for a long time. You come to use it; the tires are flat, damp has got into the electrics, maybe rusted the fuel lines; air in the brakes and the clutch plates stick.
What was once just a little rusty and neglected is now a junker. Not worth the price of a new battery. That's hysteresis.