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Thread: Experiment question..proving the law of conservation of mass

  1. #1 Experiment question..proving the law of conservation of mass 
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    Help with science experiment: proving the law of conservation of mass?

    Ok well for my homework in science class I am supposed to design an experiment that proves the law of conservation with these materials: triple beam balance; NaHCO3; vinegar; Erlenmeyer flask; balloon, water, scooplula, graduated cylinder.
    The problem is, I don't know how to make an experiment with those materials lol... If anyone could help me out a little bit here and show me how to make an experiment with these materials or even just help me a little it would be greatly appreciated.


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    Forum Radioactive Isotope MagiMaster's Avatar
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    Well, what happens when you mix the NaCO3 and the vinegar?


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    As a matter of principle, how are you going to prove the law of conservation of mass?

    You can do what you want with your chemicals, balloon etc, and observe that the total mass does not change, but you will never prove that mass cannot increase or decrease in some other situation.

    Which it does, by the way, even in your experiment (although only a very tiny amount of mass). When you mix the NaHCO3 with the vinegar, the resulting reaction will produce heat, which will be dispersed in the surrounding air (through the walls of your cylinder, balloon etc), and the mass inside will be smaller by the amount equivalent to that energy under .

    What really is conserved all the time is the sum total of mass and energy. But you cannot prove that either; we accept it in a leap of faith.
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    What really is conserved all the time is the sum total of mass and energy. But you cannot prove that either; we accept it in a leap of faith.
    I would not call it "a leap of faith". Either an experiment or a series of experiments supports conservation of mass and energy or it does not. Are you saying the foundations of science are matters of faith ??

    I understand your clarrification of the use of the word "proof" but I don't undertsand what you mean by "leap of faith" ?


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    Quote Originally Posted by MohaveBiologist
    I would not call it "a leap of faith". Either an experiment or a series of experiments supports conservation of mass and energy or it does not.
    An experiment either contradicts this law (which I believe never happens) or it does not contradict it. Laws of conservation (of mass and energy, of electric charge, of momentum etc) are negative laws - they say that something (a particular kind of change) has never happened, and never will. Such a law, by definition, cannot be proven by any number of observations or experiments, any more than you can prove your honesty by presenting a hundred witnesses who never saw you stealing (this is why, in the judiciary, the onus of the proof rests with the accuser).

    Quote Originally Posted by MohaveBiologist
    Are you saying the foundations of science are matters of faith ??
    Absolutely. Perhaps the most primordial foundation of all science is the assumption that matter will continue to behave in ways consistent with the patterns we have observed so far, since the dawn of humanity. But we have no guarrantee that the whole observable universe and all of the laws we observe in it are not a product (or byproduct) of processes occurring on some "meta" level, that will one day take another turn and change everything.

    As I mentioned a couple of times in other threads, our universe might be somebody's computer simulation - for all we know. If it were so (though I believe, without proof, that it is not), who can stop the programmer from changing a couple of header files at a whim?

    Or it might be a ripple on the surface of some huge immense humungous meagabig God-knows-how-many-dimensional hyperspherical ball of some meta-liquid, a ripple that is regular in itself, but can be disturbed at any moment by a meta-kid throwing a meta-pebble. Perhaps one such pebble was the Big Bang?

    Of course I have no evidence to support any of these far-fetched images (too crude to be called models), and I do not believe in them, or propose them as true - just as unfalsifiable.

    And even beyond that there is each person's fundamental trust in their own senses, which saves us (I mean, most of us) from sollipsism. I am not a sollipsist, but refusing to be one is, also, a matter of faith. You cannot prove to me that the whole world, inluding you, is not just my sick imagination or a dream. Or an induced hallucination, as in the movie Matrix. In fact, I cannot prove to myself that the world exists. I just believe it.
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    A better way of phrasing the problem would be to "demonstrate" conservation of mass.

    Off topic, conservation of mass/energy can be derived from Noether's Theorem and the symmetry of the laws of the universe with respect to time.
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    Quote Originally Posted by MagiMaster
    Off topic, conservation of mass/energy can be derived from Noether's Theorem and the symmetry of the laws of the universe with respect to time.
    And what grounds do you have to know (rather than believe) that those will still hold tomorrow? Or that they have not already been violated somewhere, sometime?
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    That's completely beside the point. If you keep asking why often enough, eventually you'll get to a point where no one has an answer.
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    Quote Originally Posted by MagiMaster
    That's completely beside the point. If you keep asking why often enough, eventually you'll get to a point where no one has an answer.
    So you have to accept some fundamental premise(s) as true without asking for a proof. Which is what I call a leap of faith.
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    Absolutely. Perhaps the most primordial foundation of all science is the assumption that matter will continue to behave in ways consistent with the patterns we have observed so far, since the dawn of humanity. But we have no guarrantee that the whole observable universe and all of the laws we observe in it are not a product (or byproduct) of processes occurring on some "meta" level, that will one day take another turn and change everything.
    It's a foundation based on evidence and experience NOT faith.

    Our experience so far dictates matter will behave today as it did yesterday. It does not require a "leap of faith" to make a prediction that the sun will set today as it did yesterday. IT REQUIRES A LEAP OF FAITH to suggest matter will change it's properties between yesterday and today.

    So while I do not completely toss out what you are saying the application of faith is not placed appropiately if it should be placed anywhere at all.

    If you climb and jump off a tall building rest assured you will splatter on the sidewalk and energy will be conserved .. it would require a "leap of faith" to think otherwise.

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    So you have to accept some fundamental premise(s) as true without asking for a proof. Which is what I call a leap of faith.
    I don't think this is even so .. mathematicaly the laws of physics can be prooved.

    http://www.youtube.com/watch?v=3YARP...om=PL&index=43

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    Quote Originally Posted by Leszek Luchowski
    Quote Originally Posted by MagiMaster
    That's completely beside the point. If you keep asking why often enough, eventually you'll get to a point where no one has an answer.
    So you have to accept some fundamental premise(s) as true without asking for a proof. Which is what I call a leap of faith.
    Wrong.

    In mathematics one is forced to accept a set of axioms without proof, on faith. The set is surprisingly small, the Zermelo-Fraenkel axioms of set theory plus the axiom of choice is the usual set of assumptions. Mathematics is not science.

    In science, you not have the concept of "proof", but rather you have empirical evidence that applies within some domain of validity. Science is basically a process of successive approximation, without a notion of "absolute truth".

    But in science NOTHING is accepted on faith. Physical laws are accepted on the basis of agreement with experiment, and nothing else. If a "law" is found to be in disagreement with reliable experimental data, then a better "law" is needed. No physical theory is accepted except through agreement with well-executed experiments. Once a theory has a large amount of support, then predictions based on that theory are generally thought to be true, unless and until they are contradicted by experiment. So, for instance the existence of black holes was widely accepted on the basis of predictions of general relativity, which was supported by a mountain of evidence. But that did not stop, and in fact encouraged, astronomers to look for signs of the presence of black holes in their observations -- and they found them.
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    Science is basically a process of successive approximation, without a notion of "absolute truth".
    I like the concise message in that statement.

    Yet .. some scientist .. insist that at the very end of the journey .. somewhere .. if they look hard enough there exist and they will find an absolute truth.

    Will science ever get to that point of absolute truth or get farther away the closer we get ?


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    Quote Originally Posted by MohaveBiologist
    Science is basically a process of successive approximation, without a notion of "absolute truth".
    I like the concise message in that statement.
    And I like its candidness. I am a bit surprised (in the sense that it never occurred to me) by DrRocket's statement that there is no notion of "proof" in science. It's a nice one. No irony - I really like it.

    Now how does that compare to the OP's science teacher, who told him to "prove" the law of conservation of mass using a science-fair experiment?
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    Now how does that compare to the OP's science teacher, who told him to "prove" the law of conservation of mass using a science-fair experiment?
    Careless use of terms but I'd rather deal with the OP use of "proof" then use of the term "faith".

    His experiment will provide evidence that supports the law of conservation of mass. Assuming he does it carefully and can callect and measure all the reactants and products.

    It will give him first hand experience or knowledgeof the law of conservation of mass as opposed to just reading it in a book. In a sense his experiment will add to all the other experiments that have demonstrated the conservation of mass and so it becomes a law of conservation of matter.

    I think it's a great science project.

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    Quote Originally Posted by Leszek Luchowski

    Now how does that compare to the OP's science teacher, who told him to "prove" the law of conservation of mass using a science-fair experiment?
    The OP's science teacher apparently knows little of science.

    An experiment can never "prove" a principle. It can disprove it, but finding a contradition. Or it can corroborate the principle by finding data consistent with the principle. It takes consistency in all experiments to corroborate, but not prove, a physical theory. It takes only one valid contrary experiment to disprove a theory.

    For many years all experiments seems to corroborate Newtonian mechanics. Then along came experiments like the Michelson Morley experiment that found the speed of light to be constant and not vary with the speed of the earth relative to the "absolute space" of Newtonian mechanics was disproven and a new theory, relativity had to be constructed.

    There is one other minor problem with "proving" conservation of mass. If you take mass in the usual sense, rather than as mass/energy as in relativity, then mass is not conserved. You will not find disproof in any high school experiment based on chemical reactions, but nuclear reactions do provide disproof. What is conserved is mass/energy, and you need Einstein's E=mc^2 to understand the meaning of the more general conservation law.
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    Hello Doc ..

    It takes only one valid contrary experiment to disprove a theory.
    Why so ? :?

    I would respectfully disagree ; If you can not prove it you can not disprove it. Not in science anyway. Math maybe so ..

    A contrary experiment weakens a theory it may not bring down the entire house and cause the theory to be discarded. It depends.

    What other experiments are contrary and how many experiments are not contrary to the theory ? What affect do contrary experiments have on the usefulness of the theory ? What theory will replace the current theory and is it anymore in agreement with current experiments ?

    Clearly .. there are competing theories in science neither of which may be supported by all the experimental data ?

    As you have concisely stated ; "Science is basically a process of successive approximation, without a notion of "absolute truth". "

    So an experiment contrary to the theory makes the approximation less accurate but several theories may all be competing and approximations need to be comapred. There may not be a hands down winner. No ?

    The OP's science teacher apparently knows little of science.
    .. or the OP confused the situation and put words in his teachers mouth.

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    Im sorry, but this is ridiculous. Why are you all nit-picking about the definition of 'leap of faith', 'proof' and 'absolute truth' instead of helping him with a basic experiment?

    Not the first time someone is bombarded with philosophical bickerings that dont serve anything other than to confuse the OP and make science seem like some sort of myth.

    On a lot of topics i read the people replying seem more focused on picking apart the question until it means nothing, rather than try to help the OP gain a better understanding of science.

    if someone asks why the sky is blue, whats the point in bickering over every minute detail of quantum behaviour, molecular structure and the fundametals of light. then afterwards say 'well you cant prove its blue because blue is a subjective term so the question is pointless!'.
    So i dont see why talking about mass in relativistic terms is going to be any use to the OP, or dissertations on specific words in his question.

    Suppose thats the drawback of forums on science, it doesnt matter how or what you say, there is always something that can be expanded on or be explained more accurately. hence everyone starts saying 'No, actually its like this....' and you end up with 12 pages of garbage and ego flexing.
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    Quote Originally Posted by MohaveBiologist
    Hello Doc ..

    It takes only one valid contrary experiment to disprove a theory.
    Why so ? :?

    I would respectfully disagree ; If you can not prove it you can not disprove it. Not in science anyway. Math maybe so ..

    A contrary experiment weakens a theory it may not bring down the entire house and cause the theory to be discarded. It depends.
    Of course you can disprove a theory. It far easier to disprove a theory than it is to prove one. Theory: Water is a solid at 72F. Disproof: Pour it out of a pitcher. QED

    The reason that you cannot prove a theory, is that a theory is supposed to produce true predictions of natural behavior under all relevant conditions. It is impossible to test all the relevant conditions, It is quite possible to find one set of relevant conditions under which the predictions can be shown to be wrong.

    One, just one, valid data point can invalidate a theory. This is a precise analog to the fact that in mathematics one counter-example is enough to show the invalidity of a conjecture or the existence of a mistake in the logic of a purported "theorem".

    While it is true that several experiments are sometimes required to convince oneself of the accuracy of an experiment, it only takes one reliable empirical data point to show that a theory is wrong.

    When a theory is shown to be wrong it may be retained as a good approximation in some situations, but only that. Such is the case with Newtonian mechanics, which has been demonstrated to be wrong, and replaced by a better approximation in the form of relativity and quantum mechanics. Newtonian mechanics is still used to make predictions in most situations, and it dominates engineeering. It is an excellent approximation except when speeds near that of light are involved, when there is an extremely strong gravitational field, or when the behavior of particles on the atomic scale is of interest. Nevertherless, it is known to be wrong.

    You are perhaps too close to biology. Biology has not yet developed to the point of being based on theories of sufficient predictive power and rigor to admit of testaqbility at the level of physical theories -- but it is getting there. It is the fuzziness of biological theories and of the experimental data that permits theories to only be weakened. This is really a statement of the fundamental precision of those theories at the start. Progress in molecular biology is channging this situation and propelling biology away from observation and phenomenological classivication and in the direction of greatere precision and more rigorous science. That is a good thing.

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    Quote Originally Posted by harvestein
    Im sorry, but this is ridiculous. Why are you all nit-picking about the definition of 'leap of faith', 'proof' and 'absolute truth' instead of helping him with a basic experiment?

    Not the first time someone is bombarded with philosophical bickerings that dont serve anything other than to confuse the OP and make science seem like some sort of myth.

    On a lot of topics i read the people replying seem more focused on picking apart the question until it means nothing, rather than try to help the OP gain a better understanding of science.

    if someone asks why the sky is blue, whats the point in bickering over every minute detail of quantum behaviour, molecular structure and the fundametals of light. then afterwards say 'well you cant prove its blue because blue is a subjective term so the question is pointless!'.
    So i dont see why talking about mass in relativistic terms is going to be any use to the OP, or dissertations on specific words in his question.

    Suppose thats the drawback of forums on science, it doesnt matter how or what you say, there is always something that can be expanded on or be explained more accurately. hence everyone starts saying 'No, actually its like this....' and you end up with 12 pages of garbage and ego flexing.
    Yep, I agree. There are a lot of things that you don't see.
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    Hello doc ...

    It is the fuzziness of biological theories and of the experimental data that permits theories to only be weakened.
    .. What you call "fuzziness" I call complexity

    Don't forget biology is dependent on chemistry and physics as well as math so if there is fuzziness the problem may well be in the fundamental sciences. Lately .. after spending more time in math and physics books listening to biology lectures is a bit "fuzzy"

    The reason that you cannot prove a theory, is that a theory is supposed to produce true predictions of natural behavior under all relevant conditions. It is impossible to test all the relevant conditions, ...
    Yes .. part true but also "by definition" a theory is a tentative idea because someone may come up with a better idea that may explain all the same experiments better then a previous theory and "neither" of the competing theories may be assiciated with a contradictory experiment. One is just tighter then the other in making predictions. One is "stronger" the other "weaker".

    One, just one, valid data point can invalidate a theory. This is a precise analog to the fact that in mathematics one counter-example is enough to show the invalidity of a conjecture or the existence of a mistake in the logic of a purported "theorem".
    True in the theoretical world not so true in reality. Even in physics it is possible to super cool water below freezing point. That would not invalidate the chemistry of water. It means chemistry is complex. In simplist terms .. "it depends".

    How could you disprove natural selection with a single data point and when and if anyone does the theory will not simply be discarded .. it is simply too valuable in a practical sense. It is not a matter of "right" versus "wrong".

    Biology has not yet developed to the point of being based on theories of sufficient predictive power and rigor to admit of testaqbility at the level of physical theories -- but it is getting there.
    Physical phenomana are kept simple and not as complex as biology. What makes you think nature can be painted into a corner ? The Hiesenberg principle made us think twice about the complexity of simple particles .. what complexity will we encounter in consciousness ? Again .. the weakness of biology may not be in biology itself it may be in the chemistry and physics applied within biology !!

    It is not simply a case of fuzzy data aquisition but inherent properties of that which is being studied.

    By the way .. talking with you about string theorist it looks like physics has more then it's share of fuzziness :-D

    Out of my area of expertise .. maybe you could clarrify .. but I did hear about a famous mathemetician or logician mentioned in a lecture .. I can't remember the name .. that proved .. "proved" that given a finite set of known ( axioms ?? .. not the word I wanted ) .. even then contradictions can be found in math and logic. So not even our most theoretical systems that we define ourselves are free of contradictions.

    A pleasure chatting with you.

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    Yep, I agree. There are a lot of things that you don't see.
    I agree 100 %.

    In fact it would be an injustice if we simply talked about how to collect gases with a balloon. :-D

    That is what science teachers are for :-D

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