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# Greatest physical misconceptions

## Greatest physical misconceptions

(OP)
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?

### RE: Greatest physical misconceptions

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

### RE: Greatest physical misconceptions

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

### RE: Greatest physical misconceptions

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

### RE: Greatest physical misconceptions

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.

### RE: Greatest physical misconceptions

My parents always called me 'the greatest physical misconception'

### RE: Greatest physical misconceptions

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.

### RE: Greatest physical misconceptions

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

### RE: Greatest physical misconceptions

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

There's no such thing as thermal inertia!

### RE: Greatest physical misconceptions

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.

### RE: Greatest physical misconceptions

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

### RE: Greatest physical misconceptions

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

TTFN

### RE: Greatest physical misconceptions

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.

### RE: Greatest physical misconceptions

Optimism.

It's probably not connected to much...

### RE: Greatest physical misconceptions

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

### RE: Greatest physical misconceptions

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!"

### RE: Greatest physical misconceptions

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.

### RE: Greatest physical misconceptions

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

### RE: Greatest physical misconceptions

Linked to ZDAS's post about Big Oil quashing the water fueled car, there's the variation that Big Oil have patented a water buring car/ electric car/ highly fuel efficient car, again to keep the invention from the world.

Of course a patent, is, by definition, a public document, and only runs for a limited amount of time....

### RE: Greatest physical misconceptions

It always surprises me to see how many people (engineers, even) think there is a moment of "hang time" before a dropped object begins to fall.  Too many "Road Runner" cartoons, I guess.

### RE: Greatest physical misconceptions

"Hot water freezes fater than cold water."?

Do freezers ramp up their power when the temperature goes past a certain point and work harder to bring their temperature back down?
If that was the case with some freezer designs then it might have the side effect that a glass of hot water would freeze more quickly than a glass of cold water.

### RE: Greatest physical misconceptions

Read the link.  The phenomenon has been documented for over 2000 yrs.

TTFN

### RE: Greatest physical misconceptions

It is common for people to think that vacuum does work and that "cold" flows toward warm.

Doug

### RE: Greatest physical misconceptions

Just an idle question - could you not explain every facet of thermodynamics by assuming that coolth exists rather than warmth?

I must confess I find temperature a fairly confusing concept at the best of times (cue IRstuff's lecture on freezing windscreens at night when the air temperatureis above freezing, and why a solar furnace can't be hotter than the sun)

Cheers

Greg Locock

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

### RE: Greatest physical misconceptions

What is the relative speed if I move towards you and you come forward to me, both of us at 10mph? And what if the speed is that of light?

Ciao.

### RE: Greatest physical misconceptions

Greg
I used to visualize temperature as the thermal equivalent of pressure.  Heat "deflates" towards cool.  To make something cooler requires a "heat pump" to create a "thermal vacuum".

A bit pedantic, but it helped me put a picture to many concepts.

### RE: Greatest physical misconceptions

Greg
It helps me to remember the ultimate villain, entropy.  It takes more energy to put the gasoline together then the energy released by combustion.  Thus I remember that all systems will try to move toward a less energetic state, i.e. hot will try to move to cold. (Of course, opening the refrigerator door seems to make a lie of that as you feel the cool air spill out into the warmer room)

Flamby
Similar thought.  If I was standing there watching you approach at the speed of light, would you not suddenly appear and  would seem that you would recede away from me as the images from farther away came to me. (The image of you at 0 feet would get there first, then 1 foot, 2 foot…100 yards, etc.  Even though the farther images left sooner they could not outrace you to form an image on my eye.)

JOhn

### RE: Greatest physical misconceptions

Regarding glass as a liquid, check out...

http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

They end up by not being sure exactly what a solid is.  A lot of claims about slow flow of glass are not accurate.

JHG

### RE: Greatest physical misconceptions

Very (super) cool,  It was just something I had been taught back in the early 70s
John

### RE: Greatest physical misconceptions

Wind chill--I hear people worry about not having enough antifreeze in their radiator if the wind chill will be minus 20F even though the temperature remains above 32F.

### RE: Greatest physical misconceptions

Oops. Meant to say 20F, not minus 20F.

### RE: Greatest physical misconceptions

Wind chill is a good one - I vaguely remember it was an experiment involving fit people standing around in the Antarctic and saying how cold they felt.

Oh we used to have a good one on the engine forum - ram air intakes. If you had a really big ram air intake funnelling down to a small throat then you'd get some huge compression wouldn't you?

Cheers

Greg Locock

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

### RE: Greatest physical misconceptions

in canada, wind chill is real (trust me) ...
but what many drivers do (particularly truck drivers) is they cover up most of the radiator ('cause they don't need the evaporative cooling)

### RE: Greatest physical misconceptions

epoisses, try the obvious: You leave the jug in the sink as a safety measure, if it gets knocked over you don't have a wet floor!

### RE: Greatest physical misconceptions

Wind chill is real, no doubt about it, it is the effective rate of heat transfer.  When the wind is blowing hard on a day that is near (but above) freezing, your body will give up heat at a rate that is the same as the rate on a much colder day, but if you die your body will not freeze.

If the temperature is below freezing, the wind chill will accelerate the rate at which something freezes.  Since it is below freezing much of the year in Canada (I've heard August through June, but that might have been an exaggeration), blocking the air flow has the effect of slowing the rate of heat transfer.

David

### RE: Greatest physical misconceptions

Still, as far as cars and wind chill go...

In a car that is not running, the coolant will not get colder than the ambient air temperature, regardless of wind chill.

### RE: Greatest physical misconceptions

Sorry, that was my point. The 'calibration' of the wind chill charts you normally see were produced by Antarctic explorers standing around outside in their knickers saying "gosh, it's mighty damn chilly this morning".

As soon as you add clothing, or long term exposure, or change the fitness level or the calorie intake of the subjects, you'll get different curves.

I vaguely remember that people who live in the tropics can die of hypothermia in temperatures that we'd regard as perfectly survivable.

Cheers

Greg Locock

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

### RE: Greatest physical misconceptions

1.-A bigger pipe from a elevated tank , give more pressure than a smaller one.

2.-A pump can suck far below 33 fT or 10.033 meter.

3.-Why to worry about vaccum ? , if it is only 1 Atmosphere pressure: this vessel shall resist it, an oil 205 Gl drum.

4.-If you close the output in a centrifugal pum, pressure will burst it.

And keep coming .....

### RE: Greatest physical misconceptions

When dividing approximate physical quantities expressed in whole numbers, the larger the number of digits to the right of the decimal point, the more accurate the answer.

### RE: Greatest physical misconceptions

hyposmurf's sucking pump reminded me of one I encountered recently.  A co-worker insisted that a hydraulic cylinder with the rod side open to atmosphere and piston side closed, full of oil, would hold significant tensile load.  I tried to explain that the maximum load would equal one atmosphere pressure on the rod side and more than that would draw a vacuum space on the piston side.  I don't think he believes it to this day.

### RE: Greatest physical misconceptions

Perhaps the greatest physical misconception is that USA has the engineers and resources to combat a force 4 hurricane.

### RE: Greatest physical misconceptions

Perhaps the greatest physical misconception is that USA has the engineers and resources to combat a force 4 hurricane.

It's not a question of if you have them, it's how you implement their usage.

### RE: Greatest physical misconceptions

Sometimes nature wins, and nothing can be done or implemented) about it.

### RE: Greatest physical misconceptions

Jbel is right others less so.

The US has some excellent LCACs that would have resolved the problems in New Orleans much faster however the USS Kearsarge and USS Harper's Ferry (the mother Ships) are deployed in the Gulf.  The best comment I have heard is "A man-made levee will always collapse from lack of maintenance and logical thinking".

The levees were 16-17ft but a full 4 ft lower at the points that collapsed, eroded from the bottom.  Why have a rescue centre below water level?  Police cars and other emergency vehicles were some of the first to be lost, and all this after an excellent "huricane pam" exercise in July 04 that predicded all the experienced problems.

Most of the recomendations made in 1993 (Galloway report)have not been implements.  Many of the levees have not been repaired since 1965. 1,900 sq miles of protective coastline have been lost since 1930, and lack of dredging has resulted in the Mississippi flowing on an "aquaduct" through the city.

### RE: Greatest physical misconceptions

no, but think of the peace of mind (apart from the conspiracy paranoids)

### RE: Greatest physical misconceptions

My physics may be a little rusty but what would using a datum star prove.  Isn't that just using another frame of reference (just like using a position on the earth or on the sun or anywhere in between)?  From that point of view you may measure the movements and determine from your frame of reference that the earth is orbiting the sun.  Well what if in fact the star that you are measuring from is actually orbiting the earth.  I am definitely not a geo-centrist but it seems to me that you can probably pick any point in space and call it the center of the universe and based on today's physics and math, make it work...or at least make it difficult for anyone else to refute.

### RE: Greatest physical misconceptions

if you measured the angle between the satellite, the sun and polaris, and you know you are orbiting the earth (radar distance measurement) you'd be able to determine your position in space.

i've thought a little more about this (slow day !).  geo-stationary satellites orbit with a period of 24 hrs.  if the sun is orbiting the earth with a period of 24 hrs, it would be station keeping with satellite (it would have a constant bearing, either in the sun or out of it).  i'm willing to bet that it would sense the sun only 1/2 the time.

### RE: Greatest physical misconceptions

rb1957's comment got me thinking...does the earth rotate in the geocentric model?  If not, wouldn't that mean that geo-stationary satellites are standing still in space?  I suppose one explanation could be that the earth rotates at one speed, while the sun orbits at a different speed, resulting in the 24 hr day.  Of course that would mean that all calculations relating to the altitude and velocity of geo-stationary satellites are wayyyy off, but I'm sure the geocentrists have a way of explaining that away as well.

### RE: Greatest physical misconceptions

i think they base their claim on the bible saying that the earth is stationary ...

### RE: Greatest physical misconceptions

Wouldn't it then be blasphemous (sp) to claim that man-made satellites also stand still in space while the universe rotates 'round?

### RE: Greatest physical misconceptions

(OP)
This bunch of catholics has not understood how science works. There is no such thing as "proving" a hypothesis, one can only falsify wrong hypotheses. They would not award \$1000 if we only managed to falsify their geocentrism. Somewhere down the article it says that the award is really about: "Can it be proven, by direct and irrefutable scientific evidence, that the Heliocentric system is the ONLY viable system to understand the universe." - Well of course not, as the author wrote just above that, mathematicians are so smart they can model the universe with the earth of, why not, Jupiter as the middle if they felt like. But why would they develop such an ugly, unnecessarily complicated model?

I find it unconceivable that, 5 centuries after the triumph of Copernicus' free intelligent mind over the retarded ideas imposed by the church, some people still write such kind of articles.

Anyway. Can't full moon, new moon, lunar eclipse and solar eclipse falsify geocentrism already? Or does God just hold his hand in front of it to test us...?

### RE: Greatest physical misconceptions

i think they have a model of a geo-centric solar system, with the moon and the sun orbiting the earth, and everything else orbiting the sun.

i think they can complicate their model "absurdum" to match the visual record.  yes, it results in a very complex model but i don't think science is well served by rubbishing their claims ... i'm not saying that we here have rubbished them, but rather the scientific community in general.  i also think that science is not denigrated by proving these models wrong, that this is not "beneath responsible science".

i was thinking that today we can measure the distance to the planets and as the two models (geo- and helio-centric) have very different predictions about the distance between the planets.  but then i'd expect them to claim that the "ether" affects laser light in ways we cannot understand.

### RE: Greatest physical misconceptions

Ah.

Epicycles...

Music of the spheres comes next...

As in "la la la what a load of testicles..."?

### RE: Greatest physical misconceptions

I heard somebody today refer the "speed" of gravity.  In the context of interstellar space travel.  It was stated that, and I am quoting this, that

"When we have computers that can conquer the speed of gravity we can travel anywhere in the universe because time stops."

Anyone no what the speed of gravity is?

"Education is what remains after one has forgotten everything he learned in school."  Albert Einstein

### RE: Greatest physical misconceptions

Does that matter?  I'm more curious about "time stops."

TTFN

### RE: Greatest physical misconceptions

/If/ gravity waves are real then they will have a wavespeed associated with them. Probably.

There are several experiments running to detect gravity waves, obviously non have succeeded yet.

Cheers

Greg Locock

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

### RE: Greatest physical misconceptions

It is already known fact that the gravitational force is inversely proportional to the square of the distance between two bodies and product of their masses. How fast this change occurs incase of change in the distance between two bodies or masses gives a clue about the speed of gravity. With the tangible time scales available to us, so far, this seems to be instantaneous. It is even thought that gravity propagates at speeds much greater than that of light. Here is a link to one such fascinated idea,

http://www.ldolphin.org/vanFlandern/gravityspeed.html

This link is just to give you an idea about what speed of gravity is. Nothing is guaranteed for the actual technical content. Infact, maximum members of a physics forum, in which I regularly participate, ridiculed this idea, when I posted this link there.

### RE: Greatest physical misconceptions

(OP)
Well this may or may not be a misconception, we'll know as soon as someone manages to falsify the idea (which is not the same as ridiculising it).

### RE: Greatest physical misconceptions

My very vague view is that gravity waves must be very fast, so we probably don't have a good model for them. I'm always amused by how flaky cutting edge physics is, but that's OK, we'll have a working warp drive while the physicists are still arguing about the maths. I hope.

Cheers

Greg Locock

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

### RE: Greatest physical misconceptions

It doesn’t take an engineer to know that whenever someone starts a sentence with “It doesn’t take an engineer to know” that the remainder of the sentence usually has nothing to do with engineering and is wrong.

Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion
www.kitsonengineering.com

### RE: Greatest physical misconceptions

RDK,
Same with "it's a known fact".

David

### RE: Greatest physical misconceptions

The correction in my post should be 'the gravitational force is inversely proportional to the square of the distance and directly proportional to the product of masses'.

With that, "it is a known fact" actually relates to the universal law of gravitation only or atleast I thought so. I provided the link to give mechj an idea about speed of gravity and not for its numerical value.

Anyhow, I did enjoy the excellent contradiction about saying truth. It is worth remembering.

### RE: Greatest physical misconceptions

quark : VanFlandern is generally regarded as a crank in mainstream physics circles. My understanding is that in General Relativity, gravity waves and gravity both travel at the speed of light, whereas in Newtonian physics, you have to assume that gravity travels at infinite speed, to avoid aberration effects which are known not to occur. In general relativity, for purely circular orbits, the aberration effect which would be produced by assuming a finite speed of gravity is exactly cancelled by the space curvature effect. For elliptical orbits, (which all the planets have) this does not quite happen, so the perihelion of the orbit advances slightly. It is interesting to note that Gerber got the correct answer for the advance of Mercury's perihelion considerably before Einstein did, just by assuming gravity travelled at the speed of light, but Einstein said he had made a number of mistakes and his analysis was "completely wrong". But somehow, Gerber got the right formula, and some have speculated that Einstein mucked about with his own theory until it was consistent with Gerber's result. Gerber was only a humble schoolmaster, and regarded by the mainstream as a bit of an amateur, so who knows - maybe VanFlandern has got something. But personally, I think the odds are against it.

### RE: Greatest physical misconceptions

Another misconception:
the internet is free, uncensored and unregulated -
and that it should be.
"High minded" people don't ever seem to allow for human nature.

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