4 ms·

Add air resistance into the mix, and denser materials do fall faster. Coins vs. napkins. Plums vs. crumpled balls of paper I'd actually take the lesson the oth

by GCA10 7y ago

Add air resistance into the mix, and denser materials do fall faster. Coins vs. napkins. Plums vs. crumpled balls of paper I'd actually take the lesson the other way. It's hilariously tough for model-makers to acknowledge real-world noise that prevents their theoretically precise models from delivering reliable results.

knzhou 7y ago
This is exactly why making more FCI-style questions is so hard. They shouldn't be sensitive to things like air resistance -- a question whose answer is completely changed by realistic air resistance isn't a very good one.
taeric 7y ago
I covered that with terminal velocity. And it isn't just falling, but going down a hill. Folks commonly think heavier bikes will go faster down a hill. That isn't how that works.
- marcosdumay 7y ago
  Faster bikes will go downhill faster. Both the acceleration of the bikes and their terminal velocity are determined by aerodynamics (on very steep hills) and rolling friction (on less steep ones), and those do not change much with bike weight.
- deleted 7y ago
  [deleted]
noobermin 7y ago
The reality I've learned is your intuition isn't necessarily wrong, it might just need more information. Arisotlian..."physics" isn't wrong neccessarily, it's just a model of motion under certain conditions (everyday conditions on Earth under an atmosphere or/and on friction-full surfaces) Newton's 1st can be thought of a generalization of Arisotle's (or anyone's) intuition...which to make things worse, physics' 101 students are not taught about. One of the things I think was the best ideas I learned in physics is that physics is all about approximations. Theorists tend to forget this annoyingly, but it helps keep naive scientists from using words like "fundamental" without qualifications, or saying garbage statements like "Newton's law X is wrong."
matheusmoreira 7y ago
I've done so many physics questions that explicitly instruct me to disregard air resistance... Reminds me of Feynman's speech: https://v.cx/2010/04/feynman-brazil-education https://v.cx/2010/04/feynman-brazil-education > There are no experimental results mentioned anywhere in this book, except in one place where there is a ball, rolling down an inclined plane, in which it says how far the ball got after one second, two seconds, three seconds, and so on. > The numbers have ‘errors’ in them – that is, if you look at them, you think you’re looking at experimental results, because the numbers are a little above, or a little below, the theoretical values. The book even talks about having to correct the experimental errors – very fine. > The trouble is, when you calculate the value of the acceleration constant from these values, you get the right answer. But a ball rolling down an inclined plane, if it is actually done, has an inertia to get it to turn, and will, if you do the experiment, produce five-sevenths of the right answer, because of the extra energy needed to go into the rotation of the ball. > Therefore this single example of experimental ‘results’ is obtained from a fake experiment. Nobody had rolled such a ball, or they would never have gotten those results!
- bonoboTP 7y ago
  Thanks for that Feynman link! > “If I ask you a question during the lecture, afterwards everybody will be telling me, ‘What are you wasting our time for in the class? We’re trying to learn something. And you’re stopping him by asking a question’.” In my experience there are almost just 2 types of motivated students: those who want to understand the content of the course and those who want a good grade and ultimately graduate. There's often a conflict of interest between them. For example the first group wants to learn more, ask more questions, go deeper. The second group sees this as a threat because the additional content may now be on the exam as well. And they often misunderstand this behavior of the first group as just being teacher pleasers/pets. Or from own experience: when you tell the prof that he accidentally started to cover the same topic that we already covered in the last lecture (because you're there to learn more), you will annoy a lot of people who hoped to get one fewer lectures to study in the course. Less content, less effort, same grade. You hear the first group having passionate discussions on physics or programming over a beer, while the other group discusses all the latest info of which prof is how demanding, what the grading criteria are, what the deadlines are, which departments you should or should not take courses from, where they have mandatory presence, who does multiple choice tests and who does free-text exams. I don't have much to conclude, just an observation.

by GCA10 7y ago

knzhou 7y ago

This is exactly why making more FCI-style questions is so hard. They shouldn't be sensitive to things like air resistance -- a question whose answer is completely changed by realistic air resistance isn't a very good one.

taeric 7y ago

I covered that with terminal velocity. And it isn't just falling, but going down a hill. Folks commonly think heavier bikes will go faster down a hill. That isn't how that works.

marcosdumay 7y ago
Faster bikes will go downhill faster. Both the acceleration of the bikes and their terminal velocity are determined by aerodynamics (on very steep hills) and rolling friction (on less steep ones), and those do not change much with bike weight.
deleted 7y ago
[deleted]

noobermin 7y ago

The reality I've learned is your intuition isn't necessarily wrong, it might just need more information. Arisotlian..."physics" isn't wrong neccessarily, it's just a model of motion under certain conditions (everyday conditions on Earth under an atmosphere or/and on friction-full surfaces) Newton's 1st can be thought of a generalization of Arisotle's (or anyone's) intuition...which to make things worse, physics' 101 students are not taught about. One of the things I think was the best ideas I learned in physics is that physics is all about approximations. Theorists tend to forget this annoyingly, but it helps keep naive scientists from using words like "fundamental" without qualifications, or saying garbage statements like "Newton's law X is wrong."

matheusmoreira 7y ago

I've done so many physics questions that explicitly instruct me to disregard air resistance... Reminds me of Feynman's speech: https://v.cx/2010/04/feynman-brazil-education https://v.cx/2010/04/feynman-brazil-education > There are no experimental results mentioned anywhere in this book, except in one place where there is a ball, rolling down an inclined plane, in which it says how far the ball got after one second, two seconds, three seconds, and so on. > The numbers have ‘errors’ in them – that is, if you look at them, you think you’re looking at experimental results, because the numbers are a little above, or a little below, the theoretical values. The book even talks about having to correct the experimental errors – very fine. > The trouble is, when you calculate the value of the acceleration constant from these values, you get the right answer. But a ball rolling down an inclined plane, if it is actually done, has an inertia to get it to turn, and will, if you do the experiment, produce five-sevenths of the right answer, because of the extra energy needed to go into the rotation of the ball. > Therefore this single example of experimental ‘results’ is obtained from a fake experiment. Nobody had rolled such a ball, or they would never have gotten those results!

bonoboTP 7y ago
Thanks for that Feynman link! > “If I ask you a question during the lecture, afterwards everybody will be telling me, ‘What are you wasting our time for in the class? We’re trying to learn something. And you’re stopping him by asking a question’.” In my experience there are almost just 2 types of motivated students: those who want to understand the content of the course and those who want a good grade and ultimately graduate. There's often a conflict of interest between them. For example the first group wants to learn more, ask more questions, go deeper. The second group sees this as a threat because the additional content may now be on the exam as well. And they often misunderstand this behavior of the first group as just being teacher pleasers/pets. Or from own experience: when you tell the prof that he accidentally started to cover the same topic that we already covered in the last lecture (because you're there to learn more), you will annoy a lot of people who hoped to get one fewer lectures to study in the course. Less content, less effort, same grade. You hear the first group having passionate discussions on physics or programming over a beer, while the other group discusses all the latest info of which prof is how demanding, what the grading criteria are, what the deadlines are, which departments you should or should not take courses from, where they have mandatory presence, who does multiple choice tests and who does free-text exams. I don't have much to conclude, just an observation.