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I need tips/help with physics. I just can't comprehend anything.

  1. Oct 26, 2014 #1
    Hello. I'm new here, and hopefully I didn't post this in the wrong section. But anyways, my AP Physics class is literally ruining my life. I just can't grasp the concepts, even by reading our textbook. Speaking of my textbook, it doesn't even show an elaborate step-by-step process. It jumps from step-to-step without explaining with detail. Right now, we're covering motion in two dimensions, and it's the most confusing thing ever. (I know, laugh at me because it's supposed to be an easy topic for everyone). Even motion in one dimension was hell for me. My book never explains the why and how part. For example, why and how is the acceleration of gravity 9.8 m/s2? Why does velocity and acceleration affect one another? Why is the base of that projectile-motion triangle vx = v cosθ? Why does that happen? How can that apply to real life scenarios? My textbook never explains these fundamentals, as if the book expects me to know these things beforehand. I'm aware that solving problems repetitively makes you better, but if I can't understand my textbook or even the lectures in class, then I can't jump ahead to the problem-solving.

    It's a terrible habit of mine to think like a philosopher in a strict math class. It's why I excel in creative/memory-oriented classes, such as English, History, and Art. And I'm not too bad at math; I maintain a 95% in Pre-Calculus, and same with Algebra II last year. So I don't know why physics has to be such a terrible class for me. Maybe I'm just too stupid to comprehend the concepts, or I'm not as genetically advanced as my dad, who's apparently a genius at physics. Oh, I heavily envy those who are doing great in my physics class. Anyways, you can see I let my mind wander off and get off-topic. Hooray for having a right-oriented brain. Are there any websites or books that explains physics through elaborate visuals? Any tips for surviving this 'spawn of the devil' class known as physics?
  2. jcsd
  3. Oct 26, 2014 #2
    Someone measured it and that's what it was. For example, in my high school physics class, I think we took rapid pictures of a ball falling to work out what the acceleration was. I'm not sure what the most accurate way of doing it is.

    By definition, the acceleration is how the velocity is changing.

    I'd have to draw a picture to explain it, but it sounds like you are missing some basic trig/vector ideas.

    Well, if you are playing sports or video games and that sort of thing, it often helps to understand trajectories. For example, the best way to throw a ball a long distance is to throw it up at 45 degrees. You may know that from experience or just as a fact that you learn somewhere, but physics, and in particular, the projectile motion that you are studying, explains why 45 degrees is the best.

    Sounds like you need to get a tutor or get your dad to help.

    There are probably books and websites that would help, but I'm not sure which ones at that level.
  4. Oct 26, 2014 #3

    Simon Bridge

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    The text author is expecting you to be able to think through the details. This sort of thing is usually a sg n you did not learn the foundation concepts in the earlier courses (in previous years). You should review those. Particularly you should get a tutor.

    It usually helps to make the concepts concrete by finding an open space and walking around it, or moving counters on a tabletop. But if you did not get motion in 1D, the 2D is likely to be impenitrable.

    Mathematical truths are true by definition - it's from the rules of trigonometry and so on.
    Physical truths are just true - they are descriptions of what happens in the World so there is no "why" or "how".
    The math ones you are supposed to know from your earlier education - the physical ones you just have to learn.

    Using your examples:
    This is an example of a physical truth - it just is.
    When you measure the acceleration of gravity this is what you get when you are close to the Earth's surface.
    There is a deeper way of understanding gravity that leads to this figure and other related ones. This deeper understanding forms part of a post-grad college course - you don't have the math to be able to work with that level of understanding just yet and right now that won't help you with your coursework anyway, so the text does not tell you about that.

    You are aware that lots of the World around contains objects with properties that you do not understand. Water is wet, for example. Do you know why it's wet? How it gets this property of wetness? It is unlikely you do, but that doesn't prevent you from drinking a glass of water or staying dry in the rain? Similarly, not knowing why the acceleration of gravity has a particular value should not prevent you from using the figure in calculations or understanding the consequences.

    By definition - acceleration is the rate f change of velocity.

    So you are asking: "why does the rate of change of velocity affect the velocity?"
    Well - imagine it didn't .... does it make sense to have an acceleration that does not change the velocity?
    But ... it does make sense to have a velocity that does not affect the acceleration.
    What we are doing with these concepts is working out a language we can use to describe an objects motion - and then investigating the relationships between different properties of that motion. The relationships themselves are physical truths - they have no why, they just are.

    This is a mathematical fact ... it is a fact of geometry. You learned some trigonometry last year in maths class ... that's why.

    Or do you mean - how come the speed over the ground depends on the cosine of the total speed: that boils down to how vectors add together.
    You will need to review that part of your course.

    Your book should have problems which are in terms of objects being thrown or dropped or fired from some sort of launcher (cannon or something)? Those are (simplified) real-life examples.

    What you are being taught is a tool-kit. Asking how these things are useful in real life is a bit like asking how learning to bang a nail into a bench is useful for building a house. Once you can use the basic tools, then you will be taught how to apply them to real life situations - at AP Physics you are still some way from that.

    The text author does expect you to "just know" some things. These are things the author expects you to have learned in your previous education... if he didn't do that, then your text would be much fatter. Think about it: there are others in your class - they don't seem to be having your trouble do they? Have you talked to them about it? Have you asked them how they know to do a certain thing and not something else? You'll find that they can "just know" what to do because they've done it before.

    Even so - physics is an empirical science so the real life situations are important - you can't just learn abstract stuff and hope to understand it.
    Does your school offer a practical/experimental course? Whether they do not not, when you come up with questions like this, see if you can turn them into experiments to test things out. i.e. can you come up with an experiment to check the acceleration of gravity?

    It is possible that your talents lie more in arts than in sciences and you should focus your studies in that direction rather than beating your head against this particular brick wall.
    It is tricky to identify talents in ourselves - those are the things that come easy to us so we tend not to notice that we are doing anything special.
    If you find you are doing something very easily that most other people find difficult, then that's where you talent lies.

    Not everyone is good at everything, and the World needs artists and philosophers as well as scientists and engineers.

    You won't find any one place for that ... but there are videos and animations which try to illustrate some of the trickier concepts.
    You need to isolate the particular lesson you are having trouble with - like "adding vectors" and use that as a google search term.

    You may be better to approach science through "the philosophy of science" - which I put in quotes because it's a search term you should use and a subject (a branch of epistomology) you can explore. It should help you get your head around why you are getting taught the way you are. Be warned though, philosophy is off-topic in these forums.

    Most importantly - talk to the people around you. Science is a cooperative/social pursuit which you cannot hope to do well in without contact with others. For your immediate concerns, see if you can get others to form a group to do homework together for example - and get a tutoe to help you catch up. Most schools also provide resources like supervised study rooms and catch-up courses - explore.
  5. Oct 26, 2014 #4
    Science, though, I'm good at it, such as in chemistry. So being good in science and being horrible in physics only adds to the confusion. But I want to be good in physics, and I have that strong desire to improve and refrain from giving up. I've been interested in physics since I was a child, particularly towards the physics in astronomy. I love astronomy, and I can understand the basic astrophysical concepts in my astronomy books.

    I plan on to be an aeronautical engineer after college, with degrees in aeronautics, astronomy, and physics, which only adds to my desire to improve in physics. But as you've said, I lean toward the arts rather than toward math. I'm great at Creative Writing, and it's my passion. I write short stories and novellas from time to time. The thing is, most people in the artistic field can't make a large salary. Writers need a secondary job to support themselves, and running into fame in the art field takes a huge amount of luck. Money is one of my concerns as of now; not because of greed (and hopefully I'm not sounding really greedy right now), but because I want to support myself. That is why writing, or art in general, will only be a hobby of mine in the future.

    I just can't understand how some people are great at physics, especially those who are great at it on the first day of class. The concepts are completely foreign to me, like adding vectors as you've mentioned. Physics, to me, is like learning a foreign language where you've only slept for 3 hours. I'm great at learning new languages, so I try to reinforce that perspective where physics is nothing more than just a foreign language, no different than learning Spanish or French. Not sure if it's a good way to look at it, but I also look at physics as just "art with math and numbers".
  6. Oct 27, 2014 #5

    Simon Bridge

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    From the previous - I doubt you understand the basic astrophysics concepts. That would mean you understand gravity

    You will have to use the maths lessons in geometry and vectors to understand things like vector addition and physical relationships.
    If you don't understand vector addition in physics, then you don't understand it in maths - but you claim to be good at maths - how can this be?

    You can leverage a language talent in physics - the trick is to see the mathematics as another language.
    Most Physics problems boil down to translating an English language paragraph into a maths... then applying some algebra.
    Most student struggle at this aspect so here is a place you can catch up.

    Seriously though, the people who were great at physics at the very start of class had already been doing physics before the class started.
    You can't judge by them.

    The main thing to get through to yourself here is that there is nothing wrong with you. You probably struggle at other things too - why hold physics ability in such high esteem? Perhaps because your dad does?

    You say you are good at science: then apply what you have learned - look at the situation scientifically.

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