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?

 

[IRstuff]

at least a FEW atoms ;-)

TTFN

 

[25362]

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 ?

 

[GregLocock]

I guessed the right answer, based on a long summer holding a surveyor's tape - the extra length you get by eliminating the catenary is very small.

Cheers

Greg Locock

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

 

[IRstuff]

25362,

2m/?

TTFN

 

[IRstuff]

Sorry, haven't had coffee yet.

TTFN

 

[plasgears]

One common misconception is to set the air conditioning in a space to some lower temp to cool down the space faster. The only thing you accomplish is higher energy bills and a space that is too cool and too dry. I've seen some otherwise smart people do this in public places. I coach them to 'set it and forget it.'

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.

 

[zeitghost]

That the earth is flat?

And supported by an elephant?

 

[Tobalcane]

Sometimes I wonder how the masses react when they hear the breaking news of an idea being debunked. Things like the earth being flat or the earth was the center of the universe. When Galileo try to prove that the earth was not the center of the universe, there was great opposition to a point that he was punished for the idea.

Just thinking out load…


Go Mechanical Engineering
Tobalcane

 

[minerk]

I've run into a lot of folks that are convinced that an air receiver or a water tank must have a separate inlet and outlet.

Another one is that filling a tank from the top is "easier" (requires less head from the pump) than filling it from the bottom.

 

[whyun]

Theory of Evolution as seen by believers of Intelligent Design

 

[IRstuff]

Tobalcane,

There are millions who haven't been convinced that geocentrism has been debunked yet:

http://www.edwardtbabinski.us/latest_2003/geocentrism.html

http://en.wikipedia.org/wiki/Modern_geocentrism

http://www.catholicintl.com/epologetics/articles/science/geochallenge.htm

Someone can still claim the prize offered in the last link

TTFN

 

[zeitghost]

What?

You mean there really is an elephant?

 

[Maui]

25362, yes, you are correct. The radius of the original object is irrelevant - the gap remains the same at about 0.32 meters.


Maui

Constants aren't; variables won't.

 

[rb1957]

how life being fair ? ...

sorry, that's a metaphysical mythconception

 

[rb1957]

geo-centrism ... we (being on the earth) cannot distinguish between the earth rotating around the sun, or the sun rotating around the earth ... but won't a satellite have a sufficient perspective ? ... maybe a pair of satellites (one orbiting the earth, one orbiting the sun) distance measuring between them, angle measuring to a datum star

 

[CSLufkin]

RB, I dont think the $1000 prize money will cover the satelites though!!

 

[rb1957]

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

 

[Zoobie]

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.

 

[rb1957]

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.

 

[minerk]

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.