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?
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
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
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
RE: Greatest physical misconceptions
http://catholicoutlook.com/geocentrism.php
http://w
TTFN
RE: Greatest physical misconceptions
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
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
There's no such thing as thermal inertia!
RE: Greatest physical misconceptions
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
http://w
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)
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
TTFN
RE: Greatest physical misconceptions
I don't know what you call pushing the button repeatedly for the street crossing light.
RE: Greatest physical misconceptions
It's probably not connected to much...
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
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
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
M
--
Dr Michael F Platten
RE: Greatest physical misconceptions
Of course a patent, is, by definition, a public document, and only runs for a limited amount of time....
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
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
TTFN
RE: Greatest physical misconceptions
Doug
RE: Greatest physical misconceptions
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
Ciao.
RE: Greatest physical misconceptions
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
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...
ht
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
Thanks for the heads up
John
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
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
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
RE: Greatest physical misconceptions
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
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
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
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 .....
www.cadtutorforum.net
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
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
It's not a question of if you have them, it's how you implement their usage.
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
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.
The U.S. Army Corps of Engineers requested $27 million for this fiscal year to pay for hurricane protection projects just around Lake Pontchartrain. The Bush administration countered with $3.9 million, and Congress eventually provided $5.7 million, according to figures provided by the office of U.S. Sen. Mary Landrieu (D-La.).
Just to increase the levees by 10 ft will require at lease three times the volume of fill currently used as the levee has a very narrow base and just one wall, no double barrier as used in military fortifications. Then there are the permitted chemical plants built below sea level that were just accidents waining to happen!!!!
RE: Greatest physical misconceptions
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Greatest physical misconceptions
On modern juke boxes, (they play CD's instead of records) there is a transparent tube of colored fluid with bubbles in it, but instead of the bubbles rising, they are entering at the top of the tubes and exiting at the bottom.
Not only do the bubbles go in a direction that is counterintuitive, they get larger as they approach the bottom instead of smaller as one would expect them to do due to the increase in static head.
I have been in the presence of these machines with many engineers, most of whom are smarter than me, and no one has offered a plausable explanation of what we are seeing.
Anyone got the answer?
rmw
RE: Greatest physical misconceptions
CO2 plus surfactant are an oft' attributed culprit of sinking bubbles, but a slightly different effect describes the sinking bubbles in Guinness Draught: http://www.chem.ed.ac.uk/guinness/
I've never noticed the newer jukebox bubble light traveling the wrong way... maybe a vaccum force is involved?
RE: Greatest physical misconceptions
A.
RE: Greatest physical misconceptions
Is the cooler air not denser then the warm air that it displaces, which causes the flow out into the warmer room?
John
RE: Greatest physical misconceptions
Intuitively, one would think that if the liquid was flowing from high to low, that as the pressure dropped along the length, the bubbles should grow in size. What is observed is just the opposite.
Many engineers, and some of them even good ones, have been stumped. I have yet to have one propose a solution, though.
rmw
PS: this brand of jukebox is very common in the USA, so if anyone is out enjoying a bite at an eatery that has one, go observe the phenominon.
RE: Greatest physical misconceptions
I can't explain the size change.
Mike Halloran
Pembroke Pines, FL, USA
RE: Greatest physical misconceptions
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Greatest physical misconceptions
I really don't know the answer but just posed a thought. Interesting item.
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Greatest physical misconceptions
http:/
Costas
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
Go Mechanical Engineering
Tobalcane
RE: Greatest physical misconceptions
TTFN
RE: Greatest physical misconceptions
Put a grapefruit (~5 cm radius) on the floor. Take a piece of string and wrap it around the "equator" of the grapefruit and tie it tight. Now remove the string and cut the loop. Then add EXACTLY 2 metres of string to the cut loop and re-tie it into a new, larger loop. Form this new loop into a circle and place the grapefruit at its centre. The gap between the grapefruit and the string will be big enough for you to stand in (about 30 cm or so).
Here is the clever bit. Repeat the process but instead of a grapefruit use the whole earth. Tie the string tight around the equator (assuming a flat surface), cut the loop, add 2 m, re-tie and re-centre.
How big is the gap now? Could you slide an atom through it? could you perhaps slide a human hair through it?
Highlight below for the answer
M
--
Dr Michael F Platten
RE: Greatest physical misconceptions
TTFN
RE: Greatest physical misconceptions
It appears that the "new" radius will still be longer than the original by 1m/π, namely the gap would still be ~0.3 m. Am I right ?
RE: Greatest physical misconceptions
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Greatest physical misconceptions
2m/?
TTFN
RE: Greatest physical misconceptions
TTFN
RE: Greatest physical misconceptions
Another misconception is warming up a car in the driveway. It warms up faster as you drive away at moderate speed. It also plays havoc with mileage.
RE: Greatest physical misconceptions
And supported by an elephant?
RE: Greatest physical misconceptions
Just thinking out load…
Go Mechanical Engineering
Tobalcane
RE: Greatest physical misconceptions
Another one is that filling a tank from the top is "easier" (requires less head from the pump) than filling it from the bottom.
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
There are millions who haven't been convinced that geocentrism has been debunked yet:
http://w
http://en.wikipedia.org/wiki/Modern_geocentrism
htt
Someone can still claim the prize offered in the last link
TTFN
RE: Greatest physical misconceptions
You mean there really is an elephant?
RE: Greatest physical misconceptions
Maui
Constants aren't; variables won't.
RE: Greatest physical misconceptions
sorry, that's a metaphysical mythconception
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
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
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
RE: Greatest physical misconceptions
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 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
Epicycles...
Music of the spheres comes next...
As in "la la la what a load of testicles..."?
RE: Greatest physical misconceptions
"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
TTFN
RE: Greatest physical misconceptions
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
htt
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
RE: Greatest physical misconceptions
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Greatest physical misconceptions
Rick Kitson MBA P.Eng
Construction Project Management
From conception to completion
www.kitsonengineering.com
RE: Greatest physical misconceptions
Same with "it's a known fact".
David
RE: Greatest physical misconceptions
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
RE: Greatest physical misconceptions
the internet is free, uncensored and unregulated -
and that it should be.
"High minded" people don't ever seem to allow for human nature.
JMW
www.ViscoAnalyser.com