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Seeking Advice on how to Study/Understand Physics

  1. Dec 1, 2012 #1
    Hello everyone,

    I am currently taking the first course in a series of 3 physics classics at my university. This is physics for life science majors, so it isn't necessarily too deep and integrative; it should be relatively easy.

    I took Calculus in High School/College and I am not required to do any more. So far, I have understood all the math in my physics class; that is not where I am getting hung up.

    This particular course focuses on mechanics -- we have covered motion, projectiles, FBD, friction, circular motion, gravitation, work, kinetic energy, conservation of energy, power, potential energy, momentum, collisions, impulse, center of mass, rotational dynamics, torque, and inertia.

    I am fine in understanding the problems in the context of homework, because I have all the time in the world to make sense of what is going on. However, in test situations I find myself guessing what to do most of the time. I want to be at the point where I know what is going on in the problem and I can solve it with confidence. There is a little over a week before the final; I can definitely get a high mark in the class, but I want to enhance my understanding of physics, not just for this class, but for the remainder of the series and beyond as well.

    My main issue is setting up equations. I am given the problem and I get overwhelmed by the amount of potential equations to use. I usually end up going down the wrong path.
    I am assuming that my understanding of conceptual ideas is off which is why I struggle. I should probably mention that my professor is of no help, as his lectures focus on theory and derivation of equations rather than problem solving and breaking it down for students to understand.

    I bought Schaums 3000 Solved Problems in Physics to help guide me and it has helped, but it has more supplemental value than actual lessons. Is there any website that anyone recommends to help clarify my misconceptions in mechanics and that can potentially help me understand how to set these equations myself? I know practice makes perfect and that is what I intend to exhaust for the next week, but any additional advice would be appreciated. Thank you!!
  2. jcsd
  3. Dec 1, 2012 #2
    physicsclassroom.com is a good website for understanding basic Physics concepts.

    One important thing in Physics is that you need to understand the concept behind the equations. If you know the concept it is much easier to remember the equation. You should also practice solving more problems. That would help.
  4. Dec 1, 2012 #3
    I would say that one thing which you can do is make sure you know whether the object or objects in question are accelerating. Really scan the question for indications.

    Constant velocity means the object described is not accelerating.

    Also don't go into equations immediately. Draw a diagram. I'm sure you already do that on homework but tests need the same treatment.
  5. Dec 1, 2012 #4
    From my understanding you seem to be having trouble deciding which equations to use and/or the steps you need to take to solve a problem. It's no surprise as the sheer amount of equations involved in physics makes this difficult for a lot of people my self included. The best way that to solve pretty much any problem that has math involved is to look at what you have to find and then at what you are given. First you need to know what you are are looking for and write down the equation for that. Then write down all the given and known information i.e variables and constants. (This is kinda long but I explain the steps I mentioned above through a problem. There is also a summary at the end of the post if you want to skip the problem.)
    For example take a look at this problem: (I haven't done this type of problem since grade 9 which like 4 years ago so please forgive me if I mess up)
    If an object is thrown straight upwards with a force of 100N and a speed of 19.6m/s find the maximum potential energy achieved by this object.
    So the question is asking us to find potential energy. First write the equation for that
    PE = mgh
    ok so lets write down the givens and the knowns
    F = 98.N
    V = 19.6m/s
    g = 9.8 m/s
    Now this is the part where you look at the equation for what you are trying to find in this case PE = mgh
    Here all you know is the value of g. So how can you find the values of m and h? Look at your givens you have force and velocity. Is there an equation you know where you can use either force or velocity or both to get mass? Well of course one the most basic equations in physics F = ma
    you have F = 98 and a=9.8 solving the equation gives you m = 10kg. Alright now you have one thing out of the way. So now to find h. So how can you use either F or V (your givens) to find out h. Well first you can easily figure out from the question that h has to be the maximum height reached because if the ball could go higher it wouldn't have the maximum potential energy now would it? So now you are tasked with finding the max height reached by the ball. Well you have the initial velocity of the ball and you want to find height. you also have the acceleration of the ball. If you remember in high school you might have done equations of equilibrium one of them being this
    s = vit - 1/2 at2 where s is the distance, t is time and vi is initial velocity and a = g = 9.8
    two ways to go about solving this equation you can use algebra like those guys in high school or you can go the easy and simpler way and use calculus. write the above equation as a function of time, plug in the values and find its derivative which will give you a velocity function.
    s(t) = 19.6t - 4.9t2 (multiplied a by 1/2 to get 4.9)
    v(t) = 19.6-9.8t
    max height is reached when velocity reaches zero so
    0 = 19.6- 9.8t so t = 2s. this means that the max height is reached after 2 seconds. plug this into the distance function and you get the distance as 19.6m. There you go now you have all the missing pieces you need to find PE. All that's left is to plug these values in the potential energy equation
    PE = 10*9.8*19.6 = 1920.8 J (I think I have the unit right or is it kJ I can't remember)

    So to summarize
    1) Know what the question is asking you to find and write down the equation specifically for that quantity. If you are asked to find something which can be can be found with lots of equations like mass (You can find mass using kepler's law,gravitation law, f=ma etc) then do step two first and then write down the most appropriate equation by looking at what you are given
    2) Write down all the givens and constants
    3) Find out the missing quantities from step one using your givens.
    4) plug in the quantities from step 3 into step 1 to get your answer.
    Hope this help. Again I apologize for the wall of text.
  6. Dec 2, 2012 #5
  7. Dec 2, 2012 #6
    Thank you everyone for your input; the MIT lectures are already clarifying some misconceptions
  8. Dec 2, 2012 #7
    Check out Khan Academy. Although i've never used it and can't speak from experience, it has a good reputation.

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