What are your favourite physics/mathematics misconceptions?

  • Context: Undergrad 
  • Thread starter Thread starter ergospherical
  • Start date Start date
Click For Summary
SUMMARY

The forum discussion centers on common misconceptions in physics and mathematics, highlighting the incorrect belief that "##\mathbf{F} = m\ddot{\boldsymbol{x}}## defines force." Instead, the correct interpretation is that force is a function of position, velocity, and time, as expressed in the equation ##\mathbf{F} = \mathbf{F}(\boldsymbol{x}, \dot{\boldsymbol{x}}, t)##, which must be determined experimentally. The conversation also touches on the historical context of misconceptions, such as the misunderstanding of the speed of light and the nature of quantum mechanics. Participants emphasize the importance of precise definitions and the distinction between mathematical and physical interpretations.

PREREQUISITES
  • Understanding of Newton's Second Law of Motion
  • Familiarity with classical mechanics and force definitions
  • Knowledge of spherical coordinates in mathematics
  • Basic concepts of quantum mechanics and relativity
NEXT STEPS
  • Research the implications of Newton's Second Law in modern physics
  • Explore the differences between mathematical definitions and physical laws
  • Study the historical development of misconceptions in physics
  • Learn about the role of experimental validation in defining physical laws
USEFUL FOR

Physics students, educators, mathematicians, and anyone interested in clarifying common misconceptions in the fields of physics and mathematics.

  • #61
Office_Shredder said:
This is madness. The x-y plane is defined by ##r## and ##\theta##, adding a third dimension doesn't change that. If you switch polar coordinates to ##r## and ##\phi## then I have no problem with this convention.
Well, what about the order of evaluation? I learned it a certain way, and have never thought differently about it. But there is certainly more than one way to skin a cat.
 
Physics news on Phys.org
  • #62
As a high school teacher you get to hear loads of these. (Although I teach Physics to the 16-18 yr olds I'm also sometimes required to teach general science lower down the school)

Random question from Y8 (prob G7 to many of you) at the end of a lesson on the heart and circulation: "What's the second fastest thing in the world miss after light?". While I'm pondering what to say, another one pipes up: "Miss I've heard that there are things that go faster than light, they're called quarks and they're the smallest thing you can see in a microscope". And while I'm wondering which misconception to correct first, he goes on ..."and I heard that the male testicles can squeeze the quarks and shoot them really fast so they go so many times around the body".

I went home to drink wine.
 
  • Haha
  • Like
Likes   Reactions: berkeman, weirdoguy, Astronuc and 4 others
  • #63
valenumr said:
Well, what about the order of evaluation?
I prefer whichever way makes the solution easier. Mind that you do have to do it correctly. But you really ought to be comfortable with multiple ways so you can choose the best.
 
  • #64
@rsk looks like your kids were trolling you.

Also it looks like you lived through that popular American jack-in-the-box burger commercial where the son asks a profound question to his dad and as the father is partway through the answer the kid switches topics asks another completely different profound question.
 
  • Like
Likes   Reactions: rsk
  • #65
Another one from me. You'll think I'm making it up, but I blame the IPC.

These ones were Grade 6 in a small private international school (Y7 in UK) - but I suspect that some of them were a bit younger than they should have been. Anyway, we were talking about types of energy. We get energy from food, that's chemical energy. What kind of energy do we turn it into? Movement energy. One little girl pipes up: But miss, what about skeletons?
Holy crap. I can't even remember what I said to that (she wasn't joking) but it didn't end there. Later another one said:"Miss you know sometimes when someone dies and they put them in their tomb or whatever and they come back to life again? How does that happen?"

I repeat. I blame the IPC.
 
  • #66
rsk said:
"Miss you know sometimes when someone dies and they put them in their tomb or whatever and they come back to life again? How does that happen?"
This only happens to famous skeletons, and only if someone who is alive starts it!
Newton would rotate in his grave.
 
  • Like
Likes   Reactions: jedishrfu and rsk
  • #67
rsk said:
I repeat. I blame the IPC.
Sorry, what's that? (maybe the first one on the list below?)

https://acronyms.thefreedictionary.com/IPC
1638546466492.png
 
  • #69
Plumbing code might have served them better.

It's the International Primary Curriculum. I'm not sure whether it's really to blame or whether it's just coincidence, but the schools (most international schools are 3-18 all through) I've worked at where it's been implemented have invariably been those which describe their eduation as 'innovative' and who are bigger on gimmicks than on substance.

The kids arriving in secondary from those systems have been noticeably less well prepared, both in terms of knowledge and in terms of thinking/reasoning skills. They can make a mean video on an ipad though and always with that same background music.

We are spared some of that nonsense in secondary because of the need for qualifications to access university places, yet still I've known more than one HT who spoke about ditching formal qualifications in favour of the more 'innovative' approach they claimed worked so well in primary. Those HTs just happened to be HTs in the two schools I mention where these shocking misconceptions arose and where the IPC was the system in primary.
 
  • Informative
Likes   Reactions: berkeman
  • #70
Back at the main subject: For a long time (before I thought about it ) I was worried that shaking a bottle of soda or home-brew would raise the pressure and cause it to explode. Simple physics but it absent thought it seems reasonable....
 
  • #71
As a kid, I thought we could get rid of our nuclear waste by shooting it into the sun only using the sun's gravity. Now I know, that this plan has a little momentum problem. But on the other hand, I have a new idea: why not use the waste for generating electric energy for a small magnetic field so that the radiation can be turned into an ion thruster?
 
  • Like
Likes   Reactions: Keith_McClary
  • #72
Better yet - if you have a Kerr black hole handy...

1638582177134.png


1638582192299.png


Source: MTW.
 
  • Like
Likes   Reactions: Keith_McClary and fresh_42
  • #73
fresh_42 said:
As a kid, I thought we could get rid of our nuclear waste by shooting it into the sun only using the sun's gravity. Now I know, that this plan has a little momentum problem. But on the other hand, I have a new idea: why not use the waste for generating electric energy for a small magnetic field so that the radiation can be turned into an ion thruster?
I actually saw a presentation about launching waste into orbit in the late nineties. If memory serves, putting the stuff in an orbit inside of Venus is “reasonable.” The big problem is Earth’s gravity well. Large amounts in a single launch has safety problems in case things go wrong. The proposal I saw proposed launching small volumes to get around this. Another issues is getting the material to a launch site. A lot of the waste is a sludge in decaying barrels. The total amount is extremely large in the context of moving or “processing” it for launch.
 
  • #74
fresh_42 said:
This only happens to famous skeletons, and only if someone who is alive starts it!
Newton would rotate in his grave.
What kind of angular momentum would he have?
 
  • #75
jedishrfu said:
What kind of angular momentum would he have?
About 2 Nms.
 
  • Haha
Likes   Reactions: jedishrfu

Similar threads

Undergrad Differentiating a particular integral (retarded potential)
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Laplacian of Retarded Potential: How to Derive the Equation Mathematically?
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad Change of coordinates in a potential energy field
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad What Is Four-Force in Special Relativity?
  • · Replies 44 ·
2
Replies
44
Views
6K
Undergrad Principle of relativity: active vs passive point of view
  • · Replies 29 ·
Replies
29
Views
3K
Undergrad Some notes on stochastic physics
  • · Replies 1 ·
Replies
1
Views
2K
High School What Are Common Misconceptions About Newton's Laws of Motion?
  • · Replies 36 ·
2
Replies
36
Views
6K
Undergrad What is your opinion about Freeman Dyson's opinion on the unification?
  • · Replies 16 ·
Replies
16
Views
4K
Undergrad What would a calculus author have to say on ##\int r^2dm##?
  • · Replies 11 ·
Replies
11
Views
3K
Other Leveraging engineering B.E. after pivoting to Physics - impossible?
  • · Replies 19 ·
Replies
19
Views
3K