Apples and You

 Posted by DrJeff on May 21st, 2009

 Copyright 2009  |  About this blog



This post is a Jeffism’ by Dr. Jeff and a Dr. Jeff Speaks Out.

Last time on the blog, I used astronaut John Grunsfeld’s recent Business Trip to the Hubble Space Telescope to show you that the perceived limitless ocean of air under which we live is really not limitless. At an altitude of 62 miles (100 km) above Earth’s surface, you’re effectively at the top of the atmosphere (since 99.99% of it is beneath you.) So let’s really put this in perspective with a Dr. Jeff Jeffism:


Earth’s atmosphere compared to Earth is thinner than

the skin of an apple compared to an apple.


I truly hope that makes an impression on you. Read it again and let it sink in. Then take a moment and reflect on what you’re thinking.


Now … for the rest of the story—

Our atmosphere is nothing more than a slender veil surrounding our planet. It supports all life on spaceship Earth, and its composition, temperature, and weather are clearly changing. So next time you’re in a debate about global warming, pull this Jeffism out of your pocket. It’s a simple model that provides deeper conceptual understanding, and opens up discussions about the fragility of the atmosphere and the capacity of the human race to affect it. Clearly there can be no argument that a threshold for atmospheric change exists beyond which dramatic consequences for life on Earth can be expected. The key questions: are we approaching or even past that threshold, are we causing that change, and if we are what can we do about it? We all therefore have a vested stake in this debate for we ALL have something to lose – ‘we’ the human race; and ‘we’ the other countless species of Earth.


My view? We humans are indeed the agents of global change, and that all of humanity needs to collectively consider the consequences of our actions, of our industrialization, and define a rational response – very very quickly. The diversity of life on Earth – on the savannas of Africa, in the rain forests of Central and South America, and beneath the worlds’ oceans – is at risk. All these species are voiceless in this debate, and powerless to intervene.


For a conceptually powerful educational essay on global warming as an outgrowth of human activity, read A Day in the Life of the Earth here at Blog on the Universe, or

at the Huffington Post.  It includes a foreword by Dr. James Hansen, Director of NASA’s Goddard Institute for Space Studies in New York.


Teachers and parents:

Before reading the Jeffism above to your class or child, use a familiar model to identify their preconceptions and misconceptions about the atmosphere. Get a classroom globe of the Earth and ask how high above the globe the atmosphere extends. Then read the Jeffism, and ask who’s shocked and why. Ask them to reflect on the difference between their perception of the atmosphere and reality.


Here’s more to consider:


• Have a thoughtful and interdisciplinary discussion as a class or as a family considering the larger and inter-connected issues we face on global warming in terms of: science, technology, politics, economics, funding, the need for global partnerships, ethics, and morality. Science should not be taught in isolation from all other human considerations. The world is interdisciplinary, so why would we want to teach about the world only subject by subject?


• Visit my Favorite Quotes page and read the quotes by astronaut Ulf Merbold and cosmonaut Yuri Artyukhin. How are their words relevant to the discussion?


• The Jeffism above is effective because it builds a bridge to the familiar using a model—in this case using an apple as a conceptual model to understand Earth. Read the Power of Models page to gain deeper insight into how to use modeling in learning environments, and realize that you surround yourself with countless models every day to make the world understandable.


The Experiment

Don’t let your students just assume the Jeffism is correct. Help them to insist on testing it. That’s what science is all about. Scientists (your kids) should put ideas to the torture test—and own the process. So assume my Jeffism is a hypothesis, and have them test it for themselves. And let them frame the experiment with guidance from you.


Here’s the concept: the atmosphere is 62 miles (100 km) thick and the Earth’s diameter is 7,900 miles (12,700 km). So how does Earth’s diameter compare to the thickness of the atmosphere? That’s just the ratio: 12,700 / 100 = 127. So the diameter of Earth is 127 times the thickness of the atmosphere.


What about the apple? The skin of the apple is what I’ll define as the peeling you get when you peel an apple with a good potato peeler (one that does not dig deeply into the apple). Here’s the creative thinking part of the experiment—your students/children need to propose how to measure the thickness of an apple skin. One of a number of approaches is to use a peeler to carefully peel a really long strip from an apple. Then tear off reasonably sized pieces and stack them in layers until you have a thickness you can measure with a ruler with millimeter divisions. Measure the thickness of the stack, then count the layers, and divide the thickness of the stack by the number of layers to get the thickness of a single layer. That’s the thickness of the apple skin!


Finally, measure the diameter of the apple and calculate the ratio of apple diameter to skin thickness. This ratio is what you compare to the 127 we got for the ratio of Earth’s diameter to the thickness of the atmosphere.


I just did it with a golden delicious apple. My stack of 10 layers had a measured thickness of 11 mm, corresponding to 1.1 mm for a single layer–which is the thickness of the apple skin. The apple has a diameter of 80 mm. So the diameter of the apple is only 80 / 1.1 = 72 times the thickness of the skin. Comparing that to Earth’s diameter equal to 127 times the thickness of the atmoshere means the Jeffism (at least with my apple) is confirmed!


A final thought—you can ask your students or child to go back to the classroom globe of Earth and calculate the thickness of the atmosphere on the globe. It’s just the diameter of the globe divided by 127.


Science—it’s fun, it’s a team effort, it’s eye-opening.

-Dr. Jeff


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