Do heavier objects fall faster?

Discussion in 'Physics & Math' started by mountainhare, Aug 2, 2004.

  1. Paul T Registered Senior Member

    Messages:
    460
    I agree on this. But, see below:

    The same wrong way of thought as what you did before (when you talked about accelerating rocket). A reference point for velocity must be an inertial reference frame. Earth, in this respect, become a non-inertial reference frame and therefore should not be used as a reference point. Picking a fixed point such as the origin of the objects (or the system center of mass) would not yield any differential of velocities or acceleration. That's why I said, you had picked the wrong reference point in your assessement.
     
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  3. MacM Registered Senior Member

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    10,104
    Well we clearly disagree on this .

    1 - I have yet to see anyone use a hypothetical point in space as a reference point for calculating the relative speed of a free falling object.

    If they did however then and only then would you see the acceleration and terminal velocity, time to impact, momentum, etc., always come out correctly because you would see from that vantage point not only the free-falling mass accelerate but also the earth.

    2 - All prior reference to the free-fall acceleration, etc., have been Earth.

    If you use Earth as your reference and could actually measure the minute difference doing so causes then you find that heavier objects accelerate faster and contact earth sooner.

    To try and put this issue into proper perspective.

    1 - We all agree that the mathematics are generally valid.

    2 - It is the general claim being made for the experiments and data that is false.

    The following link correctly notes the flaw regarding the fact that the earth also moves and points out that conclusions based only on the acceleration of the mass are only pseudo correct.

    3 - Since Galileo, Newton virtually all tests are stipulated for the simualtaneous free-fall of two objects side by side, in which case the conclusion is correct. They contact earth at the same time.

    4 - However, there is ample proof and evidence that tests based on earth as the reference point where it is claimed that light and heavy objects attain the same velocity in free fall to the earth are equal is invalid.

    All motion is relative. All velocity is relative and by using the earth as their reference it becomes a "0" rest reference and its motion toward a free-falling object compounds the net velocity, distance traveled/time or basis for acceleration, do not support the arguement that light and heavy objects hit the earth at the same time.

    So the math is correct but the general statement or conclusion made from that are mis-stated.

    http://encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761556362#endads
     
    Last edited: Aug 15, 2004
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  5. Paul T Registered Senior Member

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    Based on my earlier encounter with you on similar matter, where you hopelessly unable to cope with the reference frame issue, I can now understand your failure to accept my comment that you shouldn't use earth as the reference frame for case under discussion here.

    When we deal with gravitational interaction between two objects (earth and another object that we thought as free falling toward the earth), the correct -- possibly the easiest -- reference point is the center of mass of the system. Since earth is very much more massive than the falling object (say with mass in the excess of a few kgs to a few tonnes), this system center of mass is located very close to the earth center of mass. In practice, people ussualy choose earth as the reference point. But, with respect to your argument where you want to take into consideration the very tiny acceleration of earth toward the falling object, earth cannot be used as the reference point (as it move and it accelerate). The only point that we know remain unmoved is the system center of mass. Your statement that nobody use such "hypothetical" point as reference point indicate that you either do not understand the issue or you just want to defend your pointless argument.

    System center of mass is not a hypothetical point. If you understand classical mechanics well enough, you would understand that such point preserve system momentum conservation. It goes like this. There is no external force act on the two objects under gravitational interaction. Viewed by someone fixed to star far far away, those two objects gain velocity, but the whole system is stay at the same position....otherwise, momentum conservation is violated (we are not talking about such violation here). The point where the system unmoved is the system center of mass.
     
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  7. MacM Registered Senior Member

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    10,104
    Paul T,

    You can stop your preaching. We all already know what you have just said. I have also correctly pointed out the view from earth's perspective and from the free falling mass's initial drop point perspective.

    What I have said in fact is that the current trend of teaching and usage of the concept of gravity is being misrepresented. It is claimed that a light object and a heavy object falling from an equal height (excluding air, etc) will strike earth in the same amount of time. THAT IS SIMPLY INCORRECT. The heavier object will strike earth sooner.

    It is not incorrect to say the acceleration of gravity is the same for it is. The issue and the problem is that people DO use the incorrect reference when refering to the acceleration of gravity. Using the COM would make it correct.

    But re-read this thread my statements are qualified and correct. I do not have a problem with reference frames. That is your favorite distractor for a discussion to claim somebody doesn't understand and you then like to pretend to be teaching.

    QUIZ: (exclude extraneous interferences such as air resistance, etc).

    1 - So does a 1 gram object and a 10 kg object dropped from equal heights hit the ground in the same amount of time?

    2 - Does an object released from a height of 9.8 meters contact the earth in 1 second?
     
    Last edited: Aug 16, 2004
  8. Paul T Registered Senior Member

    Messages:
    460
    From the practical stand point, statement that "a light object and a heavy object falling from an equal height will strike earth in the same amount of time" is perfectly acceptable. Based on any imaginable experiment on earth, the displacement of earth is so so miniscule, much smaller than even the size of a proton. This, I would say, next to imposible for any practical measurement and therefore indicating that for any practical purposes, taking earth as the reference point and saying that those two objects would strike the earth at the same time are fairly acceptable. We know that earth also falls toward the falling object and theoretically a more massive object strike the earth surface in lesser time due to the earth moving closer to the object (although not measurable).

    Whatever you say the original problem "Do heavier objects fall faster?" remain unsolved. There is nothing fundamental about more massive object would hit earth in shorter time. We don't need any fancy theory to explain such phenomenon. Standard classical mechanics is just enough for that.

    You should know by now what my view on such problem is. My point from the start remain the same: The theoretical fact that more massive object takes lesser time to hit the ground does not mean that more massive object fall faster and therefore such argument of yours is pointless with regard to answering "Do heavier objects fall faster?"

    In case you want to know, my answer to "Do heavier objects fall faster?" is "NO". Now, I ask you: Say we dropt objects A and B consequitively (object A heavier). Will A take lesser time to fall a distance of 1m than B? Ignore variation of gravitational acceleration and any other disturbance.

    Okay, my answer is: "both A and B will take the same amount of time to fall that 1 m distance" and therefore "HEAVIER OBJECTS DO NOT FALL FASTER!"
     
  9. Nasor Valued Senior Member

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    6,221
    Well, you’re right about this. But if you want to get really picky about it you could say that it’s incorrect to teach kids that F(g)=m1*m2*G/d^2, since that doesn’t incorporate what we know about relativity. You always have to decide how much you want to dumb things down in the interest of making time for other things.
     
  10. MacM Registered Senior Member

    Messages:
    10,104
    We of course agree. But that hasn't been the issue.

    Again we agree.

    Here we only partially agree. I suspect you are correct in that it has not been proven by testing but I disagree that it is untestable. I personally have participated in tests which measured the gravity affects of 60 trillionths of a pound force.

    This is incorrect. It is indeed fundamental and inherent in current theory and mathematics if applied correctly using relativity - i.e. All motion is relative, all velocity is relative and you are measuring from earth as a reference.

    We agree properly applying current classical mechanics is all that is required to show the reality vs the false standard claim.

    Now that is interesting. You agree that heavier object hit the ground in lesser time but refuse to admit that from that perspective they fell faster. :bugeye:

    You are a self proclaimed relativists. Why do you now choose to reject relative velocity as a basis for stating a relative speed (i.e. - faster)?

    I set the trap, don't expect to lure me into it. It all depends on your definition of "fall". Its spatial distance traveled is not the same as the closure distance between the earth reference and the object.

    1 - From the perspective of earth as a reference the answer would be "Yes".

    2 - From the perspective of the COM or origin of the free-fall the answer is "No".

    I agree that the time to travel 1 m relative to the origin of the free-fall or any other fixed point in space is the same. However, that avoids the issue.

    The time to free-fall 1 m from earth to contact with earth requires less time. With earth being the standard reference, free-fall rates are now variable based on mass.

    You can only get by using earth as a reference because you are generally free-falling substantially smaller objects such that the response of earth is negligable.

    However, the point is (and has been) that this is bad science. The actual process should be taught and simply point out that for all practical purposes it may be considered equal if the mass differential is substantial and stop preaching a false concept.

    To clarify one need only consider a test of a bowling ball dropped 4.9 m in free-fall to earth and an object the diameter and mass equal to the earth being dropped in free-fall 4.9 m from the earth's surface.

    Do you still claim these two items will reach the earth consuming the same amount of time? Of course not, The heavier object will consume approximately 0.5 second not 1 second. So why make the claim light and heavy objects will free-fall to earth in the same amount of time?. It simply is an invalid statement. Teach it as it is.

    I'm glad to see you qualify your answers however, that is the correct thing to do.

    PS: I recognize that the acceleration of earth during any free-fall experiment means it is no longer a valid inertial reference since it is accelerating however, that is not taught. What is taught is that light and heavy objects hit the ground in the same amount of time from equal heights and that is false.

    The most correct thing to teach would be the COM reference and then stipulate earths motion may be disregarded in most cases.
     
    Last edited: Aug 16, 2004
  11. MacM Registered Senior Member

    Messages:
    10,104
    No the formula is fine for that level of teaching but they teach it incorrectly. I don't see that it takes that great of an effort to point out the truth of the function of the formula.

    As it is kids grow up making false claims and as you have seen here will still argue against the truth because they were mis-taught.
     
  12. Nasor Valued Senior Member

    Messages:
    6,221
    Well, if you understand the formula it's self-evident how it works. That's the beauty of formulas. Usually telling kids that light objects fall at the same rate as heavy objects is something you do at a very young age in order to correct naive misconceptions in kids who don’t know algebra yet.
     
  13. MacM Registered Senior Member

    Messages:
    10,104
    Funny how that translates into the many adults; including scientists, that will still argue that reference earth they fall to earth in the same amount of time however.
     
  14. soccerdvy Registered Member

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    3
    This is very simple... It just occured to me today, while I was sitting around the house, and I found this post as I was looking for more information on the subject. I'm 15 years old, and have never been taught anything other than "any 2 objects will take the same time to fall to Earth." It occured to me today that this is rediculous.. While both objects will accelerate towards Earth at the same time, Earth will also be accelerating towards them. Using Earth as a point of reference is completly valid for all "practical" (a word that has been used many times to defeat this argument) purposes becuase Earth is the point of impact, and the entire question is how long will it take for the object to reach the point of impact, not how long it will take to reach come in contact with a body which is no longer the center of matter...
     
  15. soccerdvy Registered Member

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    3
    Actually, you wouldn't even have to drop the two said objects at different times. You could drop them both at the same time and the acceleration of the two objects would be proportional to the sine of their masses. Consider two obejcts m1 and m2 of two distinct masses. If these two objects were to be dropped from said height H, the mean of their distance would be a point at which a line (the adjacent), running through the center of the Earth would be perpindicular to a line running through the two objects. Therefore we would have two congruent angles formed by this line, which would also be an angle bisector.
    Because it's a bisector and the adjacent side of both angles would be equal (becuase its the same segment for both angles), and the height, H, was already defined to be equal. Thanks to the side angle side theorum, we can now determine that these two triangles formed would be congruent.

    The force determined by the two masses would be this:
    F1 = ((20/3 x 10 ^ -11)(m1)(mass of earth))/h^2
    and
    F2 = ((20/3 x 10 ^ -11)(m2)(mass of earth))/h^2

    It can be seen clearly here that these two objects will have distinct Forces, based on the function of their masses. The objects will exert their distinct forces at an angle (a) determined by the equation:

    F1 sin a = distance from adjacent
    and
    F2 sin a = distance from adjacent

    It can be infered that for the two objects forces to attract the Earth to their midpoint, they would have to be at a distance from the adjacent proportional to their masses. However, because we have already determined that the adjacent would be an angle bisector, we can infer that the rate at which the Earth was attracted to each object would be proportional to the masses of the angles, and only if their masses were equal would they both hit the Earth at the same time. Since it has been determined earlier that the masses are distinct, we can gather that the two objects would fall at different rates even if dropped at the same time.
     
  16. RawThinkTank Banned Banned

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    429
    I ill b back
     
  17. RawThinkTank Banned Banned

    Messages:
    429
    I am back.

    Which will fall faster :-

    1) A tiny blackhole (with 10G) droped on earth ?

    OR

    2) Moon ?
     
  18. soccerdvy Registered Member

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    3
    trick question, there's no such thing as a black hole with a mass of 10 g becuase a 10g mass wouldn't have enough gravitational force to create a black hole in the first place
     
  19. TruthSeeker Fancy Virtual Reality Monkey Valued Senior Member

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    15,162
    I think his "G" doesn't mean "grams"....

    Besides, the mass doesn't matter. A single gram can create a black hole if it is small enough. It is not the mass that determines the black hole, it is the density - that is relationship between the mass and the space occupied by it, which is what create the gravity necessary to form the black hole.
     
  20. Nasor Valued Senior Member

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    6,221
    Whether or not something qualifies as a black hole is more a question of density then mass. In theory you could have a black hole of any mass, if you had a way to compress it enough.
     
  21. shoffsta Geek Registered Senior Member

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    60
    falling acceleration only depends on air-density, airodynamics of the object and the gravity of the planet, no more.
     
  22. FreeMason Registered Senior Member

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    75
    I would just like to point out that the argument that had they dropped the hammer and feather seperately there would be a difference in their rates of acceleration (by an unnoticeable and thus unimportant amount) is just a dumb argument.

    The conditions of the experiment are thus:

    If two objects are dropped at the same time, they will hit the ground at the same time.

    This statement is true.
     
  23. MacM Registered Senior Member

    Messages:
    10,104
    The acceleration would apear to be the same but the issue is free fall time from a given height.

    That is correct. However, that statement doesn't properly translate to the claim that all masses have the same free fall time from a given height, which was the root of the arguement.

    In fact dropping the hammer and feather at the same time results in both having an equally shorter free fall time than either independantly.

    The other issue was then how meticulus science wants to be in some areas using atomic clocks to a second in 300 years etc., but then be cavilier about gravity using overly generalized (and actually false) statements.
     
    Last edited: Dec 28, 2004

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