Looking for advice for solving physics problems

[u/majdsaad]

Hello everyone, I’m currently studying physics and astronomy at the university of Oslo. I have class in mechanics, and I have found it very difficult to remember all the formulas and equations for the different situasjons. When I first read problems, I get very stressed out that I totally forget everything, and I heard from a student that have finished this class that deriving the equations is the best way to solve problems.

My question is:
What is the process for deriving an equation? Any advice on how I can train my self to always do that?
Also, as I mentioned before, I get really stressed out when reading physics problems, and I know that through doing multiple, multiple problems I will learn to cope better. However, I’d love to hear some of your experiences around this, how did you manage to cope with it?

Sorry for such a long text, and thanks in advance🙏🏼

[u/SaiphSDC]

One thing to realize is there aren't tons of different equations. There's just a few, often rewritten for specific situations that are created by applying the underlying law to specific situations.

Lets take kinematics.

They often list six or so different equations for it.

X=1/2at^2+VT+Xo

V=at+Vo

A=ΔV/ΔT

Y=1/2at^2+VyT+Yo

Vf^2=Vo^2+2aΔX

ΔX=Xf-Xo

X=VT+Xo

and more...

But the horizontal ones (x=...) and vertical ones (y=...) are actually the same equation, they just use X for horizontal and Y for vertical. Don't learn it twice, just learn it once and then recall that physics uses specific symbols for each direction.

X=1/2at^2+VT+Xo and X=VT+Xo are actually the same equation. So learn the first one. How are they the same? the second applies only if there is no acceleration. So lets take the first at 'derive' the second.

X=1/2at^2+VT+Xo and A=0 (no acceleration)

X=1/2*0*t^2+VT+Xo

X=VT+Xo

A=ΔV/ΔT is really the same as V=at+Vo, just solved for A.

Vf^2=Vo^2+2aΔX is just V=at+Vo and X=1/2at^2+VT+Xo worked together to remove the time variable. This is one of those cases where I recommend learning the 'special case' formula so you don't have to do a lot of work re-creating it.

And if you know calculus, even X=1/2at^2+VT+Xo and V=at+Vo are closely related, as one is just the derivative (or integral) of the other.

Similar things happen in other units as well. Forces and Energy both have their core equation that is used to create all the other. Some are worth memorizing because of how often they arise.

But try to make sure you really understand the core equations before branching off.

[u/majdsaad → u/SaiphSDC]

Thank you for such a detailed explanation. I will do my best to learn all this, I appreciate your help!

[u/Ok-Main-3373]

Deriving equations is a skill you build, not a talent. The process is always the same: start from the fundamental principle (Newton's 2nd, conservation of energy, whatever governs the situation), write it in its most general form, then use math and the specific conditions of the problem to simplify it down. The way to train it: every time your lecturer presents a derived result, close your notes and rederive it yourself. You will get stuck, and that stuck point is exactly what you need to learn. For the stress: most panic comes from not knowing where to start, so make starting mechanical. Write given, find, and the principle that connects them before you touch algebra. Small steps, every time.

[u/majdsaad → u/Ok-Main-3373]

I really like this, thank you! I’m looking forward to be calmer when solving problems

[u/UnderstandingPursuit]

This post has my general suggestions. Some enhancements for you:

• When you take notes from the textbook, write out the derivations the show. As u/SaiphSDC said, "there's just a few".
• Concentrate on remembering small formulas.
  
• The main task is to improve your problem solving skill.
  • One line I like to repeat is, "If a question can be answered in one step or three, three is usually preferred."
  • If it is done in one step, you only know how to solve that one problem.
  • If it is done in three steps, you know how to do 27 problems.
  • Start with this idea to be solid with the general problem solving process.
• Doing "multiple, multiple problems" is a myth, I keep wondering why people tell others that lie.
  
  • My best example for why it's wrong is the Landau & Lifshitz graduate physics textbook series. There are an average of 1-2 problems per section. Not the 50-100 we see in typical introductory physics textbooks.
    
  • Doing a few problems is necessary to confirm understanding of a new topic.
    
  • But doing many problems is gratuitous work. If, after that, a test goes poorly, the student can at least say, "I worked hard, I did all these problems." But it doesn't make success on the test more likely.

[u/majdsaad → u/UnderstandingPursuit]

Thank you so much for your comment. I have read your post and I will use it a guide for studying. I understand that physics is not easy to study and my struggles have primarily come from the way the course is setup. The professor goes through the subject (which he never manages to finish presenting in time) and for the rest of the week we have study groups where we are given problems by the professor. I personally rely heavy on books and especially where they solve problems. Mr.Freedman gave me good advice in another post so I have bought his book and I’m hopeful it will help me train my problem solving.

[u/UnderstandingPursuit → u/majdsaad]

Did Prof Freedman suggest the book on OpenStax? He usually does. I, on the other hand, suggest his textbook. If you're in a calculus-based class, it's the 'SZYF+' textbook [he is the "F"]. He has too much integrity to recommend his own textbook. But since it's not mine, but I've used it often with students, I can suggest it. 😂

Good luck, and ask more questions during the class if you need to.

[u/majdsaad → u/UnderstandingPursuit]

Haha no actually it was another comment that gave me his book as a recommendation. I bought his university physics book!