Basic Graphing Dynamics: How Physicists Fill a Mass Plot

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Basic Graphing Dynamics: Observe Model Particles - Load Data - Answer Questions

These projects use JavaScript.

• How Data Fill a Histogram
• The Strength of Numbers in Experiments
• Information Revealed in Plotting Data

Classroom Use

Students can observe the blank histogram on the "Load Data" page. The teacher can ask students if they know what metal is in U.S. pennies. From the responses, the class can proceed under one or more hypotheses. ("They are made of copper." "They are made of zinc." "They are made of steel." "They are made of copper and nickel.", et al.)

Ordinarily, several students would probably suggest that the best way to experimentally check these hypotheses would be to break down the pennies with physical or chemical tests. At this point, suggest to them that there is an easier way. Treat the pennies as models of particles that are indivisible but that have a measureable mass.

Start loading the pennies from a sample of 150 masses onto the histogram, one year at a time from the earliest year-button on the form. They will start to accumulate near the 3.1 gram point. By the time you get into the 1970s, students will be able to see how a standard distribution is formed by real data from separate measurements of nearly identical objects.

Continue the loading year by year. In 1982, something happens. The pennies shift down in mass to near 2.5 grams; and they stay there. Assuming that originally pennies were copper throughout, and that the outside of pennies are still made of copper, a good theory suggests that there is a new component inside of pennies that is less dense than copper itself. While it may be difficult by this method alone to determine exactly what this metal is (it is zinc by the way), your students will find it possible to rule out many common cheap metals if you have a table of their densities handy.

Particle physicists often make such inferences about the insides of other particles, based on different peaks on a histogram.

A final bonus, which shows how obscure some actual data can appear, is the "Add background" button. Using it in conjunction with some of the penny buttons can give students an idea of what real data analysis can look like.

What Happens on the "Load Data" Page

The page takes some time to load. The status line at the bottom of the Netscape window shows what percentage of the loading is done. The main goal of these basic pages is to show how data fills a histogram. More refined data analysis is possible on the advanced histogram pages.

Background Information

Research scientists use the power of computers to manage data and to display meaningful images of ongoing analyses. Particle physicists are especially fond of histograms. A histogram is a kind of column graph that shows how many data fall into a specific range of values. If the data fall into these categories fairly randomly, a histogram would show:
The shape of histograms can tell the researcher when a discovery has been made. If one region seems to contain more events than can be considered accidental, then the researcher would try to account for this "bump" through further analysis.
When students collect and analyze data in the physical sciences, they often need guidance in deciding how to graph the results. If they expect a functional relationship between two measured quantities, it is generally good practice to plot the data on an xy graph, with x or y measured regularly over a range of values.

On the other hand, no relationship may seem obvious beforehand. Moreover, the investigators might have little control over the values collected except that they can measure them precisely and repeatedly. In these cases, the data might be better plotted on a histogram.