Mass or Weight? Why Students are So Confused

I observed a math lesson being taught the other day in my main placement.  Students are practicing with conversions using the following units:

ounces                                      pounds                                              tons

Students know that there are 16 oz. in a pound (lb).  They know that there are 2000 lbs. in every ton.

Then, all of a sudden, my attention was piqued when I heard my teacher refer to something which had mass as "weighing" a certain amount of grams.

AGHHHHHH!!!!!!

Having just come from Northshore Junior High where I was co-instructing in my dyad placement where we studied a unit called "Properties of Matter", I felt very sensitive and alerted to the inaccuracy of what was being said.

I took a look in the Teacher's Edition (manual/guide) to see how the authors of Math Expressions envisioned or suggested the concept of mass be addressed.  From the book, I extracted this important information:

"Compare and contrast measures of mass and weight.  Although the terms are sometimes used interchangeably, the terms do not have the same meaning.  Mass is a measure of matter--not weight.  Weight is connected to gravitational pull.  Mass has to do with density because 2 objects of the same volume may have different masses because the matter or "stuff" in one object is more densely packed than in the other--like packing more "stuff" in a suitcase of the same size.  It's the amount of matter that affects the mass/density of an object."

An extension of this idea is to consider a person who weighs 60 lbs. on earth.  The pull or force of gravity on the moon is about 1/6 that on earth.  Therefore, 60 lbs. x (1/6) = 10, and the person's weight on the moon would only be 10 lbs. (a fraction, 1/6th to be exact, of his or her earthly weight!)

This just goes to show why students come to junior high utterly confused about what mass is.  And it's a funny thing, too, because people weigh objects using scales all the time.  I stand on a scale and learn that I weight 130 lbs.  I place my backpack on the scale and realize I've been lugging around 20 lbs.  Then I place a cube of aluminum on a scale or a triple beam balance, and I measure it in grams.  Grams?  What the heck does that mean?  Kids think they are finding weight because they have done the same operations to find mass and their teachers refer to mass as weight without explaining the difference!
Wouldn't it be something to take that aluminum cube and measure its mass and then put it on a scale that measures weight (in pounds or ounces) and see how different the two really are?

Back to the space analogy.  Gravity affects weight.  But mass is unaffected because the amount of matter inside a person (or that composes a person) hasn't changed.  I am the same "me" on the moon as I am on Earth.

This idea led me to ask another question--one that I'd like answered, please!  If I take with me a triple beam balance and a cube of aluminum up to the moon and try to find the aluminum's mass, will I realistically be able to do this?  Or will the cube float away in space.  How does this work?  Now I see why understanding mass can be so problematic--the amount of matter in an object.  I'm definitely not looking at its density (although I wonder what that would feel like on the moon, too, because density is often associated with weight!).

These are a handful of questions that came out of a mass lesson that I find absolutely intriguing, and the important lesson I want to remind myself of is to NOT CALL MASS WEIGHT!  (Slugs v. Newtons)