Physical Science

Problems 2

Understanding the Past & Present, Predicting the Future


Scientists try to understand the world.  Scientists determine if their understanding is valid by making PREDICTIONS then checking if those predictions are correct.  Precise mathematical quantities are considered better predictions than vague word descriptions.  Science can't actually PROVE their understanding is TRUE.  The best scientists can do is to check predictions.  So solving problems and making predictions are essential to establish the VALIDITY of the scientific theories.  This checking against reality is the part of science that distinguishes it from philosophy.  Beyond just being a part of science, checking the predictions is the very aspect of science that makes science so valuable to civilization.  Without solving problems (i.e., making and checking predictions) you really haven't learned the skills of science.

The following problems are intended to focus your thinking, help you understand our world, and to make predictions that are verifiable.  Keep your thoughts and predictions for these problems in your journal.  Include sufficient information so you can later refer back to your journal to refresh your thoughts and memories.

  1. Chapter two introduced the conserved property of mass.  Try to list other properties of nature that seem to be conserved.

  2. As mentioned in Experiment 2-4, conservation of mass is valuable because the idea that mass is neither created nor destroyed allows us to understand what is happening when some of a process is hidden from our senses.  The following problem is one of countless examples:

    One of the common substances of our world, sulfur (abrievated S), is commercially obtained when petroleum and metal ores are refined. The sulfur is often in the form of a fine pale yellow powder although it can change form to other appearances.  One of the metals long obtained from certain ores is the brownish metal called copper (abrievated Cu).  If you mix a little copper and sulfur in a test tube, enclose with a balloon, and heat (say with a propane torch), a chemical reaction occurs producing a compound (i.e., a chemical combination) that has unique properties.  (If you try this, take care with the fire.)  Here are typical results if mass is measured like we did in Experiments 2-1 to 2-4:

    tube and balloon 20.484 g
    tube, balloon, Cu & S before heating 23.440 g
    tube, balloon, & products afterwards 23.386 g
    1. What was the mass of copper and sulfur before the reaction?
    2. What was the mass of the product after the reaction (i.e., excluding container)
    3. What was the calculated change in mass?
    4. Calculate the percent this apparent change of mass is compared to the original copper and sulfur.  Is this a significant change or more likely inaccuracy in measurement due to equipment and procedural limitations?

  3. Consider placing some clay or Playdough on one side of your balance and finding its mass with pennies or other standard masses.  If you changed the shape of the clay (or Playdough) would its mass be changed?  If you shaped it into a hollow sphere would it still balance the same standard mass?

  4. In experiment 2-1 the salt seems to disappear into the water.  What evidence is there that the salt is still there?  (In general it is a bad idea to taste substances used in experiments unless you are VERY sure all materials are edible.)  What procedure could be used to recover the salt?  (If you wish to try a procedure involving heat, be use to use a container that can withstand the heating.)  How would you expect the mass of recovered salt to compare to the original mass of salt?

  5. In Experiment 2-2 we investigated whether mass changed when ice melts.  Would the mass stay the same if you started with liquid water and froze it?  (If you try this experiment, don't fill the container full.  Leave a little room for the water to expand.)

  6. Suggest a reason for putting a lid on the container in Experiment 2-2 while the ice was melting.

  7. Sometimes scientist develop their understanding by pondering the consequences of alternative explanations.  Consider the consequences if the mass of ice doesn't change when it melts, but gains 5% when it freezes.  What would be the consequences over thousands of years when winter snow and ice melted then the water refroze the following winter?

  8. In the above situation would ice still float?
  9. How would the consequences be different in the above situation if water lost 5% of its mass when freezing but gained 5% when melting?

  10. A burning candle gets smaller.  To our senses it seems that mass is disappearing!  How could you explain the apparent loss of mass but continue to believe that mass is always conserved?

  11. Because it is hard to remember trillions of observations, we create rules that summarize what we've experienced.  We call rules such as the conservation of mass as laws of nature.  These laws are quite different from the laws created by government.  Society's laws are admonitions how we should behave.  We can choose to violate them but face being punished.  Laws of science of summaries of how nature ALWAYS behaves.  We have no choice!  We cannot violate them.  And if a violation is ever found, the law is flawed and needs to be changed to better describe Nature's behavior.  Create two columns of lists, one for laws of science you can recall and the other for laws of society.

  12. While we can't PROVE laws of science to be true, when all the pieces are shown to be logically consistent and able to explain much detailed measurements like tho few we've done, scientists gain a great deal of confidence that the laws must be correct.  Sometimes people claim to know ABSOLUTELY that an idea is right.  A 13 Century Christian, Thomas Acquinas (1225-1274), proposed that no demonstrated truth (science) is opposed to revealed truth (faith).  Acquinas established that because both ways of knowing truth come from God, scientific truth is not inferior to that provided by revelation.  Most but not all Christians accept this view.  While scientists acknowledgement that they never know anything for sure, their understanding should NOT be regarded as inferior to that claimed the absolute answers provided by faith.

If you need credit for this study, use complete sentences so that your thoughts and predictions are not just unintelligible words and numbers, but make sense to whomever is the reader.


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created 11/14/2003
revised 11/15/2003
by D Trapp
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