Greatest physical misconceptions

[epoisses]

What about a thread on the greatest fundamental physical misconceptions. They can be historical or present-day. I'll kick off with a real life example.

At home we have a jug with a water filter because the tap water is disgusting. We usually let it in the sink after filling it because filtering is rather slow. My sister-in-law who visited us the other day asked me if there was any technical reason why I put the filter in the sink (which is about 20 cm deep): "Is that to make it filter faster?". I tried to explain the special theory of relativity of height, but it didn't make it easier for her. She finally found peace when I explained it was just laziness to leave it in the sink. (She's not unintelligent otherwise although I must admit she often buys lottery tickets.)

Can anybody top that?

 

[TheTick]

Perhaps the additional gravitational force resulting from extra inches toward the center of the earth increase performance?

 

[JAE]

The strapless bra doesn't use anti-gravity paint.

 

[icelad]

Try explaining to someone that air is a fluid, glass is a liquid and that something level is not flat.

On the explaining to someone part, the best way I ve heard to explain the 3 laws of thermodynamics:

1 You cant win
2 You cant break even
3 You cant even get out of the game

John

 

[JAE]

I once read an artlicle about a physics professor (somewhere out on the west coast - can't remember his name) who was doing lots of research at a molecular level. He claimed in the article that the long held concept of atoms being little pieces of "matter", just like a little solar system wasn't correct - I specifically remember him saying something like "I can show you a proton that is 10 ft. in diameter"....basically saying that these atomic elements were waves, and not particles....but this is waaaay over this little structural guy's head.

 

[IRstuff]

Try this on for size:

http://catholicoutlook.com/geocentrism.php

http://www.catholic-forum.com/forums/showthread.php?t=2503

TTFN

 

[gaufridus]

My parents always called me 'the greatest physical misconception'

 

[25362]

The caloric theory of heat. It is a very strange substance this caloric, it has no weight but nonetheless it occupies space since things tend to expand as they heat up and shrink as they cool.

It was, I believe, Benjamin Thompson, Count Rumford who, by the end of the 18th century, ended the scientific reign of this misterious caloric fluid with the help of several cannons...

The caloric theory of heat has long since passed into the history of quaint scientific ideas, but it left us with the calorie as a unit of energy... that is, until the arrival of the joule.

 

[zdas04]

I like the conspiricy theory that "someone" has invented a car that "uses water as it's only fuel, but that big oil and big auto have squelched it (often with the added twist that they had the inventor killed)".

When you try to explain that you need a definition of "runs on water" you don't get far. If you try to provide a possible method (e.g., solar panels, batteries, electrolisis, fuel cell and/or burning hydrogen) and the reasons that you would be violating most of the thermodynamic laws that icelad so elequantly laid out for us they glaze over and accuse you of being part of the conspiricy.

Sometimes the theory comes across as a "carborator" that will allow water to be "burned". If you point out that water is occasionally used as a fire suppressant they come back with "the carborator fixes that".

David

 

[TheTick]

How about "Hot water freezes fater than cold water."?

There's no such thing as thermal inertia!

 

[GregLocock]

http://www.wiskit.com/marilyn/freezing.html

Ice cream manufacturers put their money where their mouths are and deliberately freeze warm milk to get it to freeze faster.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[quark]

The Mpemba effect was discussed in thread164-57348

http://www.physics.adelaide.edu.au/~dkoks/Faq/General/hot_water.html

Pressing down a hose at the edge to get more flowrate, or to fill a tub faster.

Perpetual motion machines

Invisibility(which is rediculed by the fact that invisible person becomes blind)

 

[rhodie]

How about the one where pushing the button on the elevator repeatedly helps get it to me faster?

 

[IRstuff]

Don't know about that, but pushing the floor buttons after someone leaves the car usually speeds up the door closing. ;-)

TTFN

 

[JimCasey]

Pushing the elevator buttons repeatedly to speed up the elevator is calles "elacceleration"

I don't know what you call pushing the button repeatedly for the street crossing light.

 

[zeitghost]

Optimism.

It's probably not connected to much...

 

[TheTick]

I'll have to back off on the water freezing thing. One day I'll have to do my own experiments.

 

[casseopeia]

Hey JAE, you might be thinking of Brian Green(e)? not sure of the spelling.

I am currently slogging through his latest book, "The Fabric of the Cosmos". Very difficult material for me. I think I read about a paragraph and a half each night.

I'll give just a few of the concepts, according to what my pea brain has interpreted.

1. All matter is made of virbating strings.
2. The particles of matter do not have a definite spin or location, just a set of probabilities. You can NEVER know, nor measure these characteristics. The very act of measuring automatically forces the particle to 'chose' the characteristic you wish to measure.
3. There is no 'space'. The concept of space is a mechanism for measuring the distance between matter. Remove all the matter and space does not exist.
4. There is no universal mesurement standard for time and space. It is dependent on the observers relative position, acceleration, place in time, etc. Hence, there is no universal truth.

I would highly recommend hearing him lecture if you can. I always leave understanding the concepts at the time, until some asks me to explain it.

"If you are going to walk on thin ice, you might as well dance!"

 

[JAE]

casseopeia,
Interesting - but on your item 4 - if there's no universal truth, then, well, then there's no universal truth to item 4 is there? a self-defeating statement.

 

[MikeyP]

A popular misconception that I come across all the time is that heavier objects fall faster than lighter ones. The reason is that 99% of the time it is true in everyday experience, due to aerodynamic effects.

M

--
Dr Michael F Platten