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Homework Help: Free-falling objects & how mass is effected

  1. Apr 5, 2009 #1
    1. The problem statement, all variables and given/known data

    How does mass affect the motion of objects falling freely under the influence of gravity? (relate to acceleration, gravity, velocity and time)

    2. Relevant equations

    This is a question that I am supposed to answer before looking at any equations. I did a lab on this but I don't think my lab reults were correct.

    3. The attempt at a solution

    My acceleration seemed to be the same for all the objects I dropped of different masses. When I released the same object from two different heights, when I dropped the object from a higher height I got a higher velocity. When i dropped two different objects of different masses from the same height, the velocity seemed to be the same. Are my observations correct or is there something wrong? What should be expecting?

    * assume we're in a vacuum
    Last edited: Apr 5, 2009
  2. jcsd
  3. Apr 5, 2009 #2
    Just curious, what were you expecting before you performed the experiment?
  4. Apr 5, 2009 #3
    I didn't know what to expect. I remember someone saying that if you dropped and feather and a hammer at the same time from the same distance they would drop to the ground at the same time so I assumed that acceleration would be the same (in a vacuum). That's all I really knew. Knowing that I would say that the difference in time would also be the same. But I'm not too sure about velocity.
  5. Apr 5, 2009 #4
    Is there anything about your experiment which you think may have been experimental error? Or do you think you did each step correctly?
  6. Apr 5, 2009 #5
    I know I have a lot of experimental error. The experiment itself wasn't carried out very carefully that's why I want to know what I should have expected so I can somehow make a comparison to my reults.
  7. Apr 5, 2009 #6
    It sounds to me like before the experiment, you expected the acceleration to be the same. After the experiment, you calculated the acceleration to be the same, but you doubt yourself.

    Just curious, what was your calculated acceleration?
  8. Apr 5, 2009 #7
    Well they were all different but they were all around 8.9-10 and I was supposed to get 9.81 correct?
  9. Apr 5, 2009 #8
    Depends on how accurate your equipment is. I usually call it 9.8.

    But yes, acceleration due to gravity is independent of mass. It's also constant (under normal conditions).
  10. Apr 5, 2009 #9
    So if acceleration is the same then the time should be the same too right? The time it takes for both objects to hit the ground?
  11. Apr 5, 2009 #10
    You can work it out mathematically if you'd like. Lets say something starts at rest from 100m above the ground.

    After 1 second, object 1 is traveling at 9.8 m/s, object 2 is traveling at 9.8 m/s
    After 2 seconds, object 1 is traveling at 19.6 m/s, object 2 is traveling at 19.6 m/s

    If two objects are accelerating at the same rate, they're moving at the same velocity. If two objects are moving at the same velocity and they start at the same point, they'll finish at the same time.

    There is no mechanism to make one move faster than the other, if acceleration due to gravity is the only force acting on the objects.

    EDIT: Object 2 is also traveling at 19.6 m/s after 2 seconds, had a typo previously
    Last edited: Apr 6, 2009
  12. Apr 5, 2009 #11
    Thanks so much :)
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