In order to conform to new ISO standards concerning weight & measurement, in 1999 Japan must comply with ISO's recommendations concerning force measurement. This started us thinking about the difference between mass vs. force.

Presently in Japan, we may use either kilogram force (kgf) or Newston as equivalent measurement units for force. But in 1999, all force measurements must be calculated in Newton, a measurement unit for force adopted to honor Sir Isaac Newton, the great scientist who completely changed mankind's concept of nature when he discovered the Universal Gravitational Force and formulated "Newton's Laws."

If you are involved with weighing and measuring or took a physics course, I bet that you have been told about the difference between mass and force. But many individuals seem to be confused about the difference, so here is your chance to test your knowledge.

Let's see how well you do on the following "True or False" questions.

1.	To help us convert our "Tensilon" universal testing machine to measure in Newton, I asked our quality person to bring me a mass of one Newton. True or False?
2.	Since I learned in my physics book that the gravitational acceleration constant was 9.8 m/sec2 in metric units, I took one kilogram of mass and calibrated the Tesilon to read 9.8 m/sec2 Newton. True or False?
3.	Assume you are an astronaut on the moon. You have a spring that requires one Newton to contract it by a centimeter on the earth. Since the gravitational force on the moon is one sixth of that on the earth, it requires one sixth of one Newton to contract it by a centimeter on the moon. True or False?
4.	I purchased a one kilogram standard weight in Tokyo where the gravitational acceleration constant is 9.798 m/sec2, and took it to St. Petersburg in Russia. Since the gravitational acceleration constant in St. Petersburg in Russia is 9.814 m/sec2, which makes the weight heavier there, I have to convert the mass to read one kilogram times 1.0016, which is 9,814 divided by 9,798. True or False?
5.	I took a pressure gauge that reads in Newton from one location to another location. Now I have to recalibrate it to suit the gravitational acceleration constant of the newly installed location. True or False?
6.	Since food on the moon weighs one sixth of its weight on the earth, an astronaut on the moon can eat six times more than he can on the earth. True or False?
7.	An astronaut wants to calibrate his force measurement equipment on the moon with a standard one Newton load cell that he brought from earth. Can he use this load cell to calibrate his equipment to one Newton on the moon? True or False?
8.	Now that ISO standards require all force measurement devices to work in Newton, can we label our force measurement load cells in Newton and sell them in the USA? True or False?
	See end of this article for answers to these questions

A Good Example of Weight vs. Mass
The other day while teaching physics to my son, I came across a good way of explaining the difference between gravitational weight and mass.

Using bread as an example, it said that even though the weight of the bread on the moon is one sixth of the weight that it would be on earth, the mass of bread stays the same. It fills you up to the same degree whether you eat it on the moon or on the earth.

Isaac Newton's Experience with Mass
When Isaac Newton was working on his theory, the definition of a mass was not so simple as we know of it today. He had to fight with the concept of levity, which was the nature of lightness. Levity is a concept that is the opposite of gravity.

Before Newton, Aristotelian scholars believed in levity as well as gravity, as they thought earth consisted of four elements: air, fire, soil and water. They felt that some materials had levity while others had gravity. For instance, a plant that grows toward the sun does so because it has levity.

Another of their interesting notions was that hell is located down under the ground, while heaven is high above. They felt that unfortunately, since man is made up of gravity elements rather than levity elements, it is easier to be pulled down rather than levitated up. Thus, they felt that it was easier for a man to go to hell than heaven. ...There may be a lot of wisdom to this thinking!

In "Philosphiae Naturalis Principia Mathematica" published in 1687, Newton did pendulum experiments using different materials as weights. By Aristotelian standards different materials should behave differently because of the essential differences in their composites.

The materials he chose for the experiments were gold, silver, lead, glass, sand, salt, wood, water and wheat. Remember your physics class where you conducted pendulum experiments with metal weights supplied by the instructor? How many people ever thought of using wheat of equivalent weight instead of the weights already supplied?

Newton had to conduct these experiments in order to dispute the concept then held by Aristotelian scholars who believed each material had its own inherent nature, resulting in a different behavior. Newton reported that they all showed the same results within an accuracy of 1 part by 1000.

He had to prove that the behavior of a mass is independent of its material content and its mass is completely proportional to its weight. That is, wheat that has the same weight as gold, behaves the same as gold. This is a contradiction to Aristotelian thought.

PS. I suggest that now that we will encounter measurements in Newton, you make sure that you intuitively know what one Newton is or how strong a force it is. Knowing each unit intuitively is as important as knowing its definition in many cases. That is the very reason why changing intuitively known units of measure to metric or somewhat artificial units by law is not easy.

Answers to above questions:
Questions 1 through 6 are all false. Question 7 is true.
The answer to question 8 involves the ingenuity of a marketing specialist and can be a very controversial question.

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