# Things People Learn Wrong in School?

• Bboy Physics
In summary, these misconceptions can lead to misunderstandings when studying or working with physics.
Bboy Physics
Hello PF!

What are some common things you see among peers in physics that they learned wrong in school? I'm talking about misconception(can you believe some college students think that the electrons are in a planetary orbit around the nucleus of an atom?!?). I'd like to avoid looking like an idiot later.

I've seen minutephysics common misconceptions video if you're planning to link that to me.

In my country,Science is being taught about wrong facts comparing to modern age but they are in historical order. As Chemistry/Modern Physics (Atomic Structures) is start with Dalton's Law dealing with Atom can't be divide but later (in upper classes) same teacher say Atoms can be divided in Electrons, Protons etc.

n10Newton said:
In my country,Science is being taught about wrong facts comparing to modern age but they are in historical order. As Chemistry/Modern Physics (Atomic Structures) is start with Dalton's Law dealing with Atom can't be divide but later (in upper classes) same teacher say Atoms can be divided in Electrons, Protons etc.

lol..

The idea that fundamental particles are spheres with some finite radius has to be one of the most prevalent.

One of the biggest things that gets me is the concept of relativistic mass, i.e. that mass increases at relativistic speeds. It's led to more than a few misunderstandings on these forums, mostly from thinking that a fast enough particle will turn into a black hole because of it.

In math, a lot of people have strange ideas about infinity or convergence. In my intro to real analysis class, the teacher asked if the set of all numbers 1/n where n is a natural number, has a minimum. Everyone obliged "yes, 0". Because 1/n "converges" to 0. People somehow think that converging means that it ACTUALLY "BECOMES" 0.

BODMAS and other similar rules (and how people, including me, thought that division and multiplication aren't of equal precedence), is creating a lot of discussion here and on Facebook.

In my grandson's elementary school science class, they did a science experiment where they rolled a solid cylinder and a hollow cylinder made of the same material down an inclined plane. The solid cylinder got to the bottom faster. The students were asked the reason for this. Their explanation was that the solid cylinder weighed more, so it got to the bottom faster. The teacher happily accepted this explanation.

On the Bob the Builder TV show, there was a fictional thunder storm, and the characters were talking about how fast the sound travels from the point of the lightning strike to where you are located. The answer was that it travels one mile every second, so if you see the lightning and then 5 seconds later you hear the thunder, the lightning struck 5 miles away. I pity the poor schoolkid who really believes this, since the danger is much closer than he thinks.

I'd also like to add that I remember in elementary how my science teacher got a plastic cup with water in it, put a postage on top of it, flipped it, and let go of the postage and it wouldn't let go(because of atm). Her explanation? The water was sticky.

On the Steve Wright show (BBC Radio 2) this past week they read out their usual list of "Factoids". If I heard correctly one was...

"The furthest you can send a DC electrical signal is 3km"

Well ok I know what they were trying to say but it's certainly lost a bit in the editing somewhere.

When I was at school (<1978) two of the subjects I studied were Physics and Applied Maths. There was some overlap which sometimes caused problems.

In physics class the syllabus taught us that friction was independant of contact area. That makes sense - you might think that increasing the contact area would increase friction but it also spreads out the load over a larger area so net effect could reasonably be zero.

However the Applied Maths syllabus seemed to use a different definition of the coefficient of friction. That required us to factor in the contact area. We did raise this contradiction with our teachers but were just told we had to remember which exam we were sitting in and answer accordingly!

We must have done because we passed with good grades.

There are a few misconception to do with electricity and magnetism...

Many people think electrons flow very fast (perhaps at the speed of light) and all the way around a circuit the instant it's switched on.

An equal number think magnets are an infinite source of energy and cite fridge magnets as proof.

Lots think that the Back EMF of a motor is the reason its not 100% efficient.

CWatters said:
There are a few misconception to do with electricity and magnetism...

Many people think electrons flow very fast (perhaps at the speed of light) and all the way around a circuit the instant it's switched on.

In my high school electricity/electronics class, we were taught this "fact".

Jimmy said:
In my high school electricity/electronics class, we were taught this "fact".

too many of us were ... me included.
Only thanks to spending a decent time on PF have I learned the error of the teaching
there's may other things too that PF have cleared up. eg...

the Big Bang WASNT a point source explosion of matter

Dave

This thread may end up being quite informative for more than a few, if only the general public would read it!

To follow on with a similar theme, I had a near on stand up argument with a Tech professor whilst doing a math portion of a Trade qualification. He was teaching us about capacitors ect ect, and mentioning that the biggest capacitors were around 1000 micro Farads. I chimed in and said you could get 1/2, 1 and upto 2 Farad for automotive sound systems. He basically said I didn't know what I was talking about and must have the sizes wrong. Also in his class around the same time, we were discussing magnets. I mentioned that home theater speakers which are placed near the tv (usually center speakers) have screened/shielded magnets to prevent image distortion on the tv. He said "No, they wouldn't have a strong enough field to effect the image. The shield would be for some other reason."
Some people just don't want to know.

Damo

There is a tendency even among physicists and good teachers, to believe something is a fact because they have a cheap explanation for it. Sometimes the explanation is wrong and sometimes even the fact is wrong.

Stuff that comes to mind:
(wrong theory)
- The wire with weights cutting through a block of ice. It is often used as an example for a shift of the melting point under pressure. As far as I remember the correct explanation had something to do with thermal transport and molecular surface effects
- Bicycle pumps as an example of gas heating under compression when it is mostly friction otherwise the tires would get just as warm
- constant travel time around the airplane wing explains lift

(wrong facts)
- Resonance catastrophe stuff: Bridges collapsing due to soldiers marching has never been reported
- same for singers breaking wine glasses (at least it doesn't work for non defective glasses)
- the different areas of taste buds don't exist but children are encouraged to prove the teacher by testing it
- whole grain bread turning sweet while chewing due to enzymes turning starch into sugar (usually this type of bread is so sour that you won't taste any sweetness)

I am sure that there are many more...

The only one that comes to mind is the answer to "What do we need Algebra for?"
The standard math teacher answer is not that good, and sounds like,
You have to have it to do higher level math,(very true, but not complete.)
The best answer I ever heard went like this.
"Numerical data comes in all forms, often that form is not useful.
Algebra is a methodology for converting data from an unusable form to a usable
form, and being assured of the results."

water conducts electricity.

I don't remember ever being taught this, but am sure a teacher or few have said so as a matter of fact.

One of the worst things you can ever be taught is that you can expect to be given the best, up-to-date answer to all Science questions. You just could not handle it all in one go. That's why you can expect to be given the 'historical' story, starting with concrete stuff that could be called 'wrong' but is often just a simple approximation to the truth.

Also, before we start enjoying slagging off school teachers for their lack of Science knowledge, let's consider that they are probably not PhDs in many of the subjects that they are expected to deliver to their pupils. They are possibly not specialists in any academic subject at all and they have, first and foremost, to entertain and control a room full of little oiks who don't particularly want to learn anything and would rather chat and have fun. Any effort they have left over can be used for actually teaching.

There is also a problem with the Curriculum that schools are expected to deliver. Hitting kids with the Particle theories of Light, Electricity and Heat early on in their Science has really blighted their ability to deal with those three subjects. No one understands what a Photon is but they blithely bring them into all sorts of 'explanations' about the way the world works. Politicians, who never 'got' or applied the Scientific method in their work, are the ones who set the agenda for Science teaching.

BTW The Millennium Bridge over the River Thames had to be closed because of people-assisted-resonance from the crowds walking across it. People were falling over from it. The resonance was cured by adding mechanical damping. (Not a wrong fact)

And, if it were not for the duff things we were told early on, there'd be not point in having PF, on which we can all feel smug about sussing things out so well.

sophiecentaur said:
One of the worst things you can ever be taught is that you can expect to be given the best, up-to-date answer to all Science questions. You just could not handle it all in one go. That's why you can expect to be given the 'historical' story, starting with concrete stuff that could be called 'wrong' but is often just a simple approximation to the truth.

Also, before we start enjoying slagging off school teachers for their lack of Science knowledge, let's consider that they are probably not PhDs in many of the subjects that they are expected to deliver to their pupils. They are possibly not specialists in any academic subject at all and they have, first and foremost, to entertain and control a room full of little oiks who don't particularly want to learn anything and would rather chat and have fun. Any effort they have left over can be used for actually teaching.

There is also a problem with the Curriculum that schools are expected to deliver. Hitting kids with the Particle theories of Light, Electricity and Heat early on in their Science has really blighted their ability to deal with those three subjects. No one understands what a Photon is but they blithely bring them into all sorts of 'explanations' about the way the world works. Politicians, who never 'got' or applied the Scientific method in their work, are the ones who set the agenda for Science teaching.

BTW The Millennium Bridge over the River Thames had to be closed because of people-assisted-resonance from the crowds walking across it. People were falling over from it. The resonance was cured by adding mechanical damping. (Not a wrong fact)

And, if it were not for the duff things we were told early on, there'd be not point in having PF, on which we can all feel smug about sussing things out so well.

Teachers and media who, knowingly or unknowingly, convey incorrect information to our youth are doing them a great disservice. It is their job and responsibility to provide correct information. That's what they are getting paid for. If they were physically abusing students, we would all be shocked. This isn't as bad, but it is not acceptable either.

- same for singers breaking wine glasses (at least it doesn't work for non defective glasses)

Mythbuster did this. It's on video, on netflix or youtube for anyone to see.

CWatters said:
When I was at school (<1978) two of the subjects I studied were Physics and Applied Maths. There was some overlap which sometimes caused problems.

In physics class the syllabus taught us that friction was independant of contact area. That makes sense - you might think that increasing the contact area would increase friction but it also spreads out the load over a larger area so net effect could reasonably be zero.

However the Applied Maths syllabus seemed to use a different definition of the coefficient of friction. That required us to factor in the contact area. We did raise this contradiction with our teachers but were just told we had to remember which exam we were sitting in and answer accordingly!

We must have done because we passed with good grades.

Yes I remember numerous exercises, tending towards the pointless as I saw it later, about friction.

I think the real problem and diseducation here is that we were being a trained to jump through hoops and be able to answer exam questions. There was not that minimum amount of philosophy which I think is needed.

Thus we were not explained the different kinds of things which get called scientific 'laws'. The difference and the relations between a fundamental law which laws of friction are not, and a phenomenological law, of much more limited validity which they are. They were quite indistinctly things we had to learn almost by heart. A false vision.

Which reminds me and gives me an opportunity to say, in part due to the above pressures, what we observe or "see" can be very much influenced by the theories and explanations we have. I think it may be Kuhn or someone who points out that watching a swinging pendulum, Aristotelians see that it slows and stops. That is what it is trying to do and that is what he sees; there are some irrelevant swings on the way. The Newtonian remembers Galileo in Florence and sees the essentially unending oscillations which, irrelevantly diminish and die out if you wait too long. He will then see this everywhere, e.g. in pendulum clocks. But a few centuries later people will not see this pendulum, they will see an example of nonlinear dynamics with a limit cycle. In which the limit amplitude depends not on initial conditions but on the parameters of the system. Perhaps the philosopher sees that Galileo made a mistake in thinking he had proved anything about pendulums - the only conclusion authorised would be that his heartbeat was rather regular that day during the service. But then may come along the historian who may say that would not have been the productive way of thinking at the time, so he was right to be wrong.

When I was a kid in grade school, we didn't have air conditioning in schools yet, so when the hot weather arrived, we would make paper fans and use them to cool ourselves off. The teachers never failed to tell us that if you fan yourself like that, you are using more energy to fan yourself than you are removing by the fan blowing air over your skin. So the net effect is that it's going to make you hotter. This explanation never worked for me, since I always felt cooler when I fanned myself. I don't know whether my third grade teacher was an expert in convective heat transfer with evaporation, but I sort of doubt it. Still, she was willing to thrust this old wives tale upon us, just because she didn't like the idea of us fanning ourselves in school. She may actually have believed it. Now, as an experienced engineer, I know that not much of my body energy is converted to heat in moving the fan back and forth, and lots of energy can be removed from our skin by blowing air with a fan (provided the relative humidity of the air is not too close to 100%). But generations of school children were allowed to swelter, and, more seriously, were misinformed.

could you guys please post the correct explanations as well? :>

Chestermiller said:
Teachers and media who, knowingly or unknowingly, convey incorrect information to our youth are doing them a great disservice. It is their job and responsibility to provide correct information. That's what they are getting paid for. If they were physically abusing students, we would all be shocked. This isn't as bad, but it is not acceptable either.
That's right as far as it goes but how much TAX would you be prepared to pay to ensure that all kids were taught everything by highly educated specialists (who would expect appropriate pay and conditions) who are also trained and selected adequately for the teaching job? About 1/60 of the population is a teacher of some sort. Paying them twice as much as they're paid now would involve an average increase in tax contributions over the population of around 1% per head. That would mean probably 4% extra tax for average wage earners. No pain no gain or do you thing that the 'blame' culture can solve the problem?

sophiecentaur said:
BTW The Millennium Bridge over the River Thames had to be closed because of people-assisted-resonance from the crowds walking across it. People were falling over from it. The resonance was cured by adding mechanical damping. (Not a wrong fact)

The mechanics of that case are quite interesting, because the mechanical feedback made the people sync their motion with the bridge, and technically it did never collapse. Telling soldiers to march out of sync would not have helped in that case because people synced up their motion involuntarily.

mrspeedybob said:
Mythbuster did this. It's on video, on netflix or youtube for anyone to see.

After going through something like 30 glasses until he found a defective one, almost touching it with his lips.

Ok Maybe these facts are more true than false. Eigenmodes do exist and resonance phenomena as well. Engineers do design with that in mind to keep buildings stable in storm and earthquakes. The Tacoma Narrows Bridge collapse is much more impressive in my opinion.

If teachers would say poorly constructed bridges or glasses with slight defects can break in extreme cases I wouldn't have any issues. Anyhow my main problem is, that people believe this stuff not because they know facts but because they have a fitting explanation.

Damo ET said:
To follow on with a similar theme, I had a near on stand up argument with a Tech professor whilst doing a math portion of a Trade qualification. He was teaching us about capacitors ect ect, and mentioning that the biggest capacitors were around 1000 micro Farads. I chimed in and said you could get 1/2, 1 and upto 2 Farad for automotive sound systems. He basically said I didn't know what I was talking about and must have the sizes wrong. Also in his class around the same time, we were discussing magnets. I mentioned that home theater speakers which are placed near the tv (usually center speakers) have screened/shielded magnets to prevent image distortion on the tv. He said "No, they wouldn't have a strong enough field to effect the image. The shield would be for some other reason."
Some people just don't want to know.
As far as I know, those powerful, affordable supercapacitors are a very recent development, they (probably) did not exist at the time the professor became professor.
Strong, big magnets got cheaper as well.

Damo ET said:
This thread may end up being quite informative for more than a few, if only the general public would read it!

To follow on with a similar theme, I had a near on stand up argument with a Tech professor whilst doing a math portion of a Trade qualification. He was teaching us about capacitors ect ect, and mentioning that the biggest capacitors were around 1000 micro Farads. I chimed in and said you could get 1/2, 1 and upto 2 Farad for automotive sound systems. He basically said I didn't know what I was talking about and must have the sizes wrong.

From http://www.sonicelectronix.com/cat_i6_capacitors.html: "If a vehicle has dimming headlights when music is played, a capacitor could solve that problem."

I have so many problems with this idea. For one thing, are you absolutely sure you heard the professor correctly? Surely you must be deaf by now!

And if your headlights are dimming when the music is playing, I think it means you have way too much audio system for your vehicle! And everyone sitting next to you at the stoplight probably thinks so, too!

But his was a silly statement unless he was limiting his comments to your normal home electronics. Try working at a high power space radar site that's bouncing 5 MW pulses off of space objects. They have what's essentially a small room of huge capacitors in parallel for each radar beam.

sophiecentaur said:
That's right as far as it goes but how much TAX would you be prepared to pay to ensure that all kids were taught everything by highly educated specialists (who would expect appropriate pay and conditions) who are also trained and selected adequately for the teaching job? About 1/60 of the population is a teacher of some sort. Paying them twice as much as they're paid now would involve an average increase in tax contributions over the population of around 1% per head. That would mean probably 4% extra tax for average wage earners. No pain no gain or do you thing that the 'blame' culture can solve the problem?

If it were only 4%, I would definitely be willing to pay more to ensure that all kids were taught properly.

Chestermiller said:
If it were only 4%, I would definitely be willing to pay more to ensure that all kids were taught properly.
I think you wouldn't find a politician who would seriously propose that and expect to be returned at the next election. You need to get real about this. Would you really be prepared to spend say \$£200 a year for the rest of your life so that other people's kids would be taught better? I can think of dozens of other people who would not be. (Most Republican voters in the US and Conservatives in the UK, for a start.)
I have been similarly disappointed with the scant levels of knowledge of many teachers (not only Science) in the UK but I think that many of them are the wrong targets for complaints about that. The requirements for specialist subject knowledge are very lax for teachers and there is very little ongoing subject training. Yes there are some very uninterested teachers but general conditions in many secondary schools are not conducive to self education. The path towards personal promotion away from the chalk-face is far more attractive for the brightest and best.

I wasn't necessarily "taught" anything wrong, but was told by teachers many, MANY wrong facts...which ends up being the same thing. Big thing I learned was that teachers are often times wrong, and when they are it's that much harder to persuade them to believe this.

Biggest one I remember is being told in Earth science that water spins the other way when flushing in the suthern hemisphere than in the northern hemisphere. Took me years to realize this. Luckily it was easy to make an experiment to convince me of the wrongfullness of this fact. Some of my friends still couldn't be convinced, even with the experiment.

Lsos said:
I wasn't necessarily "taught" anything wrong, but was told by teachers many, MANY wrong facts...which ends up being the same thing. Big thing I learned was that teachers are often times wrong, and when they are it's that much harder to persuade them to believe this.

Biggest one I remember is being told in Earth science that water spins the other way when flushing in the suthern hemisphere than in the northern hemisphere. Took me years to realize this. Luckily it was easy to make an experiment to convince me of the wrongfullness of this fact. Some of my friends still couldn't be convinced, even with the experiment.

The statement is certainly true for large bodies of air (Cyclones, depressions etc. are big enough for Coriolis to have an effect) . It's just that your average bowl of water is too small and the perturbations are too great.

mfb said:
As far as I know, those powerful, affordable supercapacitors are a very recent development, they (probably) did not exist at the time the professor became professor.
Strong, big magnets got cheaper as well.

That's my excuse. So much is changing so fast.

For someone 50+ years old, 10 years is a blink of an eye.

---------------------------------
ps. I'm now invested in a super-capacitor company, and just bought 300+ super-magnets.
Whoopie! Electro-magnetic experiments and Ouch!

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