Ask HN: How can I start learning physics?

[J-H]

Hi, I'm a high schooler who wants to learn physics but our high school doesn't offer anything past a very beginner physics course. How do I start learning - Khan Academy? or something else? Tips from anyone who learned physics thoroughly? I'm looking for something free or pretty cheap (so not really print textbooks)?

[ninthfrank07]

I recommend you the "Intro to Physics: Landmarks in Physics" course made by Udacity (http://www.udacity.com/overview/Course/ph100/CourseRev/1). I'm currently halfway through it and I'm having a lot of fun doing it! Here's the syllabus of the course:

Unit 1: How can we measure the circumference of the Earth? Basics of geometry and trigonometry

Unit 2: How do objects move? Data analysis and kinematics

Unit 3: What causes motion? Forces, acceleration, and Newton’s Laws

Unit 4: How can we use motion? Work, energy, and simple machines

Unit 5: How can we determine our longitude at sea? Simple harmonic motion

Unit 6: What is electricity? Charge and electric fields

Unit 7: What is left to discover? Modern physics and open questions

[masterzora]

http://www.staff.science.uu.nl/~hooft101/theorist.html is a great starting point. That page is written and maintained by a Dutch Nobel Prize winner who believes that it should be perfectly possible to learn physics from the internet if you know what you're looking for. If you go down the page he also includes references to print texts but the idea is for the web links to be sufficient.

[mhartl]

I taught the physics core curriculum at Caltech for five years, so I'll do what I can to help. For many of the classes at Caltech, we never found a truly satisfying textbook, but when you're learning on your own that's still the route I recommend. This means putting textbooks back on your list for consideration. Buying a textbook for a full 1-2 year college-level physics sequence costs less than $200, much less if you buy used. You have parents, right? Now they know what to get you for your birthday.

Your immediate goal should be to get a firm grounding in classical physics, which will be important for everything else you do. When choosing a textbook, the most important thing is to pick one that's aimed at scientists and engineers. That means it should be calculus-based, "algebra-based physics" being a contradiction in terms. If you don't know calculus, you should start there. (This will set you back some more money. Sounds like a plan for Christmas, Hanukkah, etc.)

To my knowledge, none of the introductory texts are truly great, but I did some poking around and University Physics by Young, Freedman, and Ford looks like a good bet. If you need to learn calculus, Calculus by Larson and Edwards looks decent. Get the most recent editions if you can afford them, but I'm sure older editions are fine. Those two books alone should take you a year or two to consume, and they are likely to be very challenging unless you have an exceptional preparation in mathematics. But even if you get stuck occasionally, you'll still be way ahead of the curve. (I wish someone had put a calculus-based physics textbook in my hands when I was in high school. I would have been unstoppable. Unfortunately, though it now seems impossible, I went to high school before Amazon or even the Web, so it simply never occurred to anyone.)

I recommend supplementing the textbooks with liberal use of Khan Academy videos and Wikipedia articles. More than anything, it is essential to solve a large number of exercises. Developing a good physical intuition is important, but physics is a quantitative discipline, which means being able to do calculations.

One more thing: if you want to demonstrate your competence to the world (and to college admissions committees), it's a good idea to take the AP Physics exam (B or C) at some point. The AP Physics C exam is the best one to target if you only have enough time to take one, as it will let you test out of introductory courses at many schools. (Not at Caltech though—we have a separate system of placement exams.) Take a look at the AP Physics C website to see the syllabus. If you decide to take the exam, buying a test-prep book such as 5 Steps to a 5 AP Physics B&C is probably a good idea. If you go this route, try to negotiate with your school to get course credit for your independent study.

P.S. At some point, read The Feynman Lectures on Physics. FLP doesn't make for a good introduction, but after you have a foundation it's gold.

[khyryk → mhartl]

I used Calculus (4th edition) by Larson, Hostetler, and Edwards for my calc 1 and 2 courses and I would not recommend it for independent study.

Consider Calculus by Briggs and Cochran instead ( http://www.amazon.com/Calculus-Early-Transcendentals-Briggs-... ) for good explanations with example problems and for the superior images, which are particularly helpful for multivariate calculus.

[manglav → khyryk]

Another calculus and all around math guide is here for free. http://tutorial.math.lamar.edu/ I've been using it ever since I was in high school. To this date, I have only rarely had to pay attention in my math classes due to this resource. This will take you to calc 4 and even cover linear algebra. The best part is he progresses in a methodical way, everything is downloadable in pdf format, and his examples are great.

For physics, the Feynman lectures are a great once you have a bit of foundation, but really any course from MIT OpenCourseWare or Coursera will do. The key is definitely doing examples, and I find it is particularly useful to apply it to real life by asking questions. Rainbows? Cameras? Bubbles? Spear-fishing? All great examples of optics. Deep sea excavations? Pulling out the Titanic? Diesel-filled bags? Perfect for studying bouyancy and forces. Have you played Tanks? (seeing as you're in high school, I'm sure you have. If not, you should!) Projectile motion! Just keep your eyes open.

Since you're doing it on your own, I highly suggest learning physics Calc based, instead of algebra based. Everything will tie in very nicely, seeing how calculus was apparently invented FOR physics (courtesy of Professor Covault at CWRU).

Kudos, and good luck!

edit: After trying to use Wikipedia for physics in college, I don't recommend it if you're trying to learn. They use weird terminology, and sometimes weird notation. Sometimes it is good for examples though. Also, check out the International Baccalaureate exams, an alternative to AP. The main difference is that AP expects lots of breadth and little depth, vs IB is vice versa. My physics teacher used to say "IB wants you to be able to answer a question the same way someone with a PhD in the field would". You can find practice exams online. By the way, for Higher Level (HL) exams (equiv to C-level in AP), around a 65% is a 7, the best score you can get.

edit2: Don't forget public libraries! Especially at large colleges or universities. They have many textbooks available, even the old ones at times (which I prefer, there's something about picking up an old textbook and learning from it that's not captured anywhere else. It feels like you're learning from the major players in the game, and I get more motivated to do well). I'll stop with the edits now.

[mhartl → khyryk]

Thanks for the calc rec. I learned calculus over twenty years ago, so I was flying by instruments on that one.

[ivan_ah → mhartl]

I second everything said here. All very good advice.

Just one thing:

> introductory texts [...] University Physics by Young, Freedman, and Ford [...] to learn calculus, Calculus by Larson and Edwards [...] should take you a year or two to consume [...]

I disagree. Two years? I think six months should be enough time for the modern youth to learn all of first year physics, calc one and two included.

The only limiting factor is the time it takes to do the exercises, because, like you said, the main part of learning physics happens when you are figuring things out on your own. I bet that one or two semesters with a good book with exercises with answers in the back can be enough to learn how to use all of first year math and physics. If only there were such a book that teaches calculus, mechanics, E&M and linear algebra, all in one sitting. ;)

I will close on a personal recommendation from 1914. Calculus Made Easy by Silvanus P. Thompson http://www.gutenberg.org/files/33283/33283-pdf.pdf

[bcuccioli]

Depending on how ambitious you are, for a more rigorous introduction to basic mechanics I recommend Kleppner & Kolenkow. Though if you choose to start with a more basic book like University Physics I strongly recommend K&K as a second book. This assumes you have passing familiarity with calculus.

[joshlegs]

You could always take the Newtonian approach and just sit under an Apple tree ...

[vitus → joshlegs]

And develop calculus, no less :)

[codeonfire]

You can get University Physics 11th edition, which mhartl suggested for about $35 used.

This will be about 1500 pages and 40 chapters. If you do a chapter per week with problems, you will know basic physics in 3/4 of a year. However, you're going to need to learn calculus as well, so pick up a used calculus book.

This is by far the cheapest route. A couple of books, some paper and pencils. My problem with online video courses are that they are SLOW. They take a tiny bit of subject matter that would fill a single page and stretch it out to a 45 minute video. It's far worse if the teacher is a slow speaker. A good solid book is open road, fast as you want to go learning.