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I'm sad

  1. Nov 22, 2012 #1
    I just read the book understanding gravity and I tried to do the math problems in them newtons law of gravity f=ma and I got completely lost. I didn't understand what he meant by an object at rest exerts the same amount of force as an object falling. I didn't understand the math about it. I guess I'm just not cut out for this, and I should just learn my place. I want to be a physicists but I guess I'm just going to have to be satisfied being a struggling single mom, with no passion.
     
  2. jcsd
  3. Nov 22, 2012 #2

    Evo

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    Staff: Mentor

    It's not for everyone, so don't let it get to you. Find something that you are good at.
     
  4. Nov 22, 2012 #3
    Keep your chin up! I'm no physicist, but as I understand it, an object in a gravitational field exerts a force in the direction of the field proportional to it's mass and the acceleration due to gravity, so for a 10kg mass sitting somewhere on earth the force is equal to 10kg * 9.8ms/s = 98 newtons.

    Notice that when calculating this force there is no reference to the objects velocity, so whether it is at rest, or moving, the force applied to the object is the same, 98 newtons in the direction of the gravitational field, which is towards the center of the earths mass.

    The difference is that an object in freefall, for example, will continue accelerating because there is no opposing force to slow it (ignoring air resistance), but an object on the ground has an equal and opposite force applied to it causing it to remain 'at rest' and not fall through the ground.

    Maybe I fluffed a few things but it's important to take the equation for what it is, a force measure, it's not measuring how much you think you weigh while freefalling, it's measuring the force applied to a body due to gravity.
     
    Last edited: Nov 22, 2012
  5. Nov 22, 2012 #4

    MarneMath

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    Education Advisor

    Well, I wouldn't worry about it too much. I did the same thing before I took a physics course and felt a bit 'confuttled' after reading it. I didn't have the skill of reading the English language and translating it into math. It's a skill that can be acquired so don't give up. Heck I failed my first physics course ever, but after some time I learned from my mistake and ended up passing every course afterward.

    So with that said, my general advice is to spend more time learning math and reading physics. Ask questions here and always remember everyone has struggled somewhere along their career path.
     
  6. Nov 22, 2012 #5
    Looking back, it took me quite a long time to understand those Newton equations so I had to practice to a lot. Even after my high school physics, I still didn't understand them that much. It wasn't just me but all my classmates too, our first year class midterm average was 15-30% even though midterm covered only these motion and force equations. But more time we spent with them, more comfortable we got.

    You wouldn't understand things just by reading a chapter unless you are superwoman. It takes time :smile:
     
  7. Nov 23, 2012 #6

    Evo

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    Staff: Mentor

    Oh, I just thought maybe she'd find something else she excelled at.

    Nevermind.
     
  8. Nov 23, 2012 #7

    So I think I understand somewhat. When an object is at rest it uses the the same amount of force as when it's falling unless you put pressure on that object. For instance I just slapped someone recently, before people go off I had every right to slap this chic, I will explain it later. My hand had force behind it so it accelarated the speed which made it hurt more. I don't want go get kicked off so I will explain the slap.
     
  9. Nov 23, 2012 #8

    Astronuc

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    Staff: Mentor

    Wanting to be something, e.g., physicist, indicates something of a passion.

    Physics is not readily intuitive for many folks, but it can be learned over time.

    Hyperphysics provides a nice and relatively simple background covering many concepts.

    http://hyperphysics.phy-astr.gsu.edu/hbase/newt.html

    http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

    PF is also a good place to learn.
     
  10. Nov 23, 2012 #9
    When you find the next thing to be passionate about, will you give up on it too at the first difficulty?
     
  11. Nov 23, 2012 #10

    No I'm sticking with this, I was just frustrated and wanted to vent.
     
  12. Nov 27, 2012 #11
    You can forever expand your understanding, even if it's by small increments. Don't give up.

    You may need to read about or listen to or discuss a concept in 10 or more places before you understand it.

    You may have to read listen/discuss it more than once.

    You may not understand it until you are done reading, perhaps while you are doing something else.
     
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