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Homework Help: F = MA & Gravity?

  1. Dec 17, 2011 #1
    1. The problem statement, all variables and given/known data

    Well, i am wondering the impact gravity has on any word problems involving a given acceleration. For instance, if a baseball weighs 1 kg and it accelerates at 2 m/s^2 what is its force?

    2. Relevant equations
    f = ma

    3. The attempt at a solution

    Would the force = 1 * 2 or would it equal 1(2 + 9.8) ?

    additionally, in general am I going to want to add gravity to all force = ma problems? Thanks!
  2. jcsd
  3. Dec 17, 2011 #2
    F=ma is actually ƩF (sum of forces) = ma
  4. Dec 17, 2011 #3
    hm, so then the force would equal 1(9.8 + 2) ?
  5. Dec 17, 2011 #4
    why do you put 9.8? since the given acceleration is already 2...
    And in fact you need to speak for VECTORS which means that magnitude alone does not give the full information needed.
    If you speak for directions, then you can know if you can "add" or not.
  6. Dec 17, 2011 #5
    I'm confused whether or not you need to add gravity. I'm a high school student, taking an introductory physics course, so I am still learning the basics, but so far my professor stresses that gravity is an acceleration. So I figured you need to add it to the given acceleration. Am I completely wrong?
  7. Dec 17, 2011 #6
    depends on the motion.
    When someone is introducing quantities like force, acceleration, velocity, displacement , etc stops talking about magnitudes alone (like mass) but speaks about direction as well.

    It is what we call vectors.

    You add them when they are parallel, you take their difference when they are anti-parallel, and when they have a general angle between them you use the Pythagora's Theorem.
    Last edited: Dec 17, 2011
  8. Dec 17, 2011 #7
    I see, well right now we're strictly doing one dimensional forces.
  9. Dec 17, 2011 #8
    Still think of what happens when you throw something towards the ceiling. It will fall down because of gravity, while you gave it an initial velocity against the gravity.
    What happens when you drop something towards the ground. It will fall faster. Etc.
    That way you can think about - or + (antiparallel/parallel).
  10. Dec 17, 2011 #9
    + what iRaid said:
    Sum of Forces= m *Sum of Accelerations

    So you can devide sum of forces in its components: F1,F2,F3,.... in how many you have, which are caused by the accelerations A1,A2,A3,..... how many you have.

    (F1+F2+F3+....)= m (A1+A2+A3+...)
    here you have 2...
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