Author Archives: Bob Tinker

Bungee Physics

Last week, Paul, Ed, and I did physics. This is such a rare event that it deserves note. We actually developed a theory, collected data, compared theory to data, came up with new ideas and tested them. We only wish kids everywhere could have the same experience.

This investigation was prompted by Ewa Kedzierska’s presentation at the World Conference on Physics Education in Istanbul in early July*. She presented a student activity on bungee jumping that claimed that the jumper falls faster than a free-falling object. This seems difficult to believe, in spite of video data she presented—collected and graphed by the wonderful COACH software—that clearly showed this to be true. We immediately thought of many reasons why this should be impossible. Imagine jumping without a tethered Bungee cord—jumper and cord would fall in free-fall just as Galileo proved in his famous Tower of Pisa experiment (never mind the fatal consequences—this is physics!). Attaching the far end of the Bungee rope would seem to apply an upward force that could only slow the jumper, not speed her up!

As typical science skeptics, we had to do it ourselves and understand the mechanism, if the effect was true. Following the maxim that was current when CERN supposedly found neutrinos travelling faster than light—“Extraordinary results require extraordinary evidence”—we needed to do the experiment ourselves and get a feel for the situation. So Ed  gathered a stepladder, chain (substitute Bungee), tennis ball (for the jumper), and a camera that takes 240 frames per second, and we collected data.

Paul, ever the theoretician, showed that the far end of a horizontal chain link held steady at the near end would fall faster than a free body, and hence, could impart some force to the falling chain. Thus, each chain link, on reaching the bottom of the “U” formed by the falling links, could impart a bit of force on the falling side and make it fall faster than free-fall. Another way of saying this is that each link, when brought to a halt, rotates 180 degrees and can exert some torque on the falling side.

We collected the data, and clearly saw the effect. It is real! And it is huge when the falling mass is small. We photographed side-by-side tennis balls, one attached to a chain and one in free fall. The one with the chain fell faster! Every time. The picture shows a frame from a movie of the experiment, clearly showing Paul about to fall (he didn’t), and the free-falling ball going slower.

Don’t believe us? Do it yourself. We attached a force sensor to the end of the chain and could detect the force from individual links. The force increased non-linearly and dramatically. Stopping the last link required 50 N even though the entire chain weighed only 4 N (see graph). We are still arguing about why the force increases so much for the last few links.

I noticed that sometimes if the falling part of the chain is close to the tethered part, the links at the bottom of the “U” do not rotate, but slide. When they slide, they do not rotate and, hence, should not accelerate the falling chain. We could hear the difference, but our results were inconclusive, because near the end of the fall, the chain doesn’t fall evenly and this causes it to revert to the link-rotation mode.

In our next blog, we’ll present the data and our analysis. Stay tuned.

Reconnecting with Ton Ellermeijer at WCPE

I recently attended the modestly named World Conference on Physics Education in Istanbul. One of the highlights of the meeting was connecting with my old friend Ton Ellermeijer and meeting his colleague, André Heck.

Some of the most innovative developments in educational technology have been made during the last 25 years at the AMSTEL Institute at the University of Amsterdam, The Netherlands, under the direction of Ton Ellermeijer. At this university, Ph.D. students in physics and other sciences could specialize in education at the Institute, which was on a par with more traditional areas of physics research. Sadly, a new dean eliminated AMSTEL in 2010. Ton soldiers on from a nonprofit he founded in 1987 (Foundation CMA), but with a reduced staff.

AMSTEL developed extensive probeware for real-time data acquisition, as well as several generations of COACH, software for analyzing these data, modeling, control, video data capture and animations. This technology has been integrated into STEM instruction using well-designed and tested materials. One area in which they have done particularly interesting work is sports physics using video analysis. Widely used in Europe, this material is unknown in the U.S., which is a great loss.

André Heck worked with Ton for a decade and published nearly 60 scholarly articles on various aspects of this research. This wealth of material has recently been collected in André’s Ph.D. thesis.The print version of the thesis comes with a CD ROM that includes all these articles as well as considerable student materials.


How to Teach About Climate?

Global temperatures in the year 2010 are on course to be the highest ever in 130-year record. This is the consensus of recent three different analyses by NASA, National Oceanic and Atmospheric Administration’s National Climatic Data Center and a joint record kept by Britain’s Met Office and the University of East Anglia. While these results do not prove that the long-term trend will continue, the conclusions add to a growing mountain of data and models that do predict catastrophic global temperature rise over the next half-century. Scientists who specialize in climate have carefully weighed all the evidence and an overwhelming number agree.

A snapshot of the stylized model of the atmosphere and oceans that students can investigate from the High Adventure Science activity on Climate Change. Programmed in NetLogo  by Bob Tinker.
A snapshot of the stylized model of the atmosphere and oceans that students can investigate from the High Adventure Science activity on Climate Change. Programmed in NetLogo by Bob Tinker.

There is a rising chorus of “deniers,” people who deny the data and projections. These are not skeptics who look at the data and draw serious opinions. Serious skepticism is an important part of science. The deniers are “contrarian scientists, free-market think tanks, and industry [spokesmen, who have] created a paralyzing fog of doubt around climate change.” The deniers claim, without proof, that the scientific case has not been made, that certain scientists are lying, even though investigations have cleared them, assert that climate change is benign, and even claim that the covenant God made with Noah will protect us. This is not science, it is propaganda.

The public is confused about these public debates and is increasingly convinced that they reflect true scientific uncertainty. Gallup polls show the percent of the population that thinks that the seriousness of global warming is generally exaggerated has grown from 30%in 2006 to 41% in 2009.

It is important to go to the root of the problem: a poorly educated nation that is unequipped to tell the difference between science and propaganda. An example of what is needed is an engaging activity we created on climate that is designed to help students understand the possible causes of climate change and appreciate the issues involved. Our key innovation is an interactive model that incorporates many of the important factors that influence climate such as clouds, CO2, water vapor, ice sheets, ocean absorption of greenhouse gasses. Students can learn for themselves about the interactions of these factors by experimenting with the model. The model is not intended to be predictive—that requires the most powerful computers that exist—but it does illustrate many of the dynamic features in the scientist’s models.

Materials based on this model should help students understand the science, but science educators need to go one step farther and help students understand the difference between science and propaganda. We need to engage students in thoughtful debate about the issue so they can form their own opinion. We should care less about what those opinions are than that they are backed by an understanding of the science and the process of science. This is why every student needs a better understanding of science.

U.S. Does Poorly in Math and Science. Again.

Today yet another international comparison reaffirmed that the United States is failing to prepare its students to compete successfully in the new flat world. PISA, the Program for International Student Assessment, was administered to 15-year-old students last year by the OECD (Organization for Economic Cooperation and Development). This is a highly respected group whose conclusions are sound and reliable.

The results of the PISA assessments showed the U.S. performance in math, science, and reading is mediocre compared to stellar performance by most Asian and European countries. In the first time participating in this exam, Shanghai students stunned the world by taking first place; in math they scored 600 on a scale for which the average was 497 and the U.S. scored 487.

Unless dramatic measures are started now, in one decade America will be unable to turn to its talented workers, inventors, scientists, and financial wizards to rescue the country from debt, pollution, and soaring energy costs. This is a national security issue as important as any.

We know how to fix the problem. The President’s Council of Advisors on Science and Technology (PCAST) recently issued a comprehensive plan for addressing the problems in mathematics and science precollege education. They provide a detailed blueprint for tightening standards, improving teacher preparation, and exploiting technology for new, research-based curricula, assessment and professional development.

The cost of the PCAST recommendations would be at most $0.3B per year. This is a trivial expense compared to the total Federal budget of $3,550B (0.008%) or even the National Science Foundation budget of $7.4B (4%). The Sustainable Defense task force has shown how we could save $100B/yr from the Defense budget with no reduction in military security, 300 times what PCAST needs.

One may wonder why the $100B already spent annually on education at the federal level is insufficient to fund the PCAST agenda. The quick answer is that there is an inbred fear of a national curriculum that would impinge on State’s rights and local control. Thus, the Department of Education is not allowed to create curricula. PCAST addressed this concern by advocating that any curricula created be available in three versions and be freely available online so that it could be modified. PCAST also recommends that a mission-oriented organization be created to implement its recommendations—not the Department of Education, which is not allowed to, or the NSF which is research oriented.

Is it impossible to imagine that Congress would fund any new initiative given the tax and budget cutting frenzy in Washington? One group looking at the rather terrifying future is the Administration’s bipartisan Deficit Reduction Panel, which just released a report “Moment of Truth” that shows how to balance the budget while still supporting educational initiatives like PCAST. It says, “At the same time, we must invest in education, infrastructure, and high-value research and development…”

Perhaps this latest PISA results will push lawmakers to finally focus on meaningful improvements in our educational system. It would be good politics, inexpensive, and absolutely essential to our national security.