This post is a Dr. Jeff’s Weekly Challenge and a Teachable Moment in the News.

Ok, I know you’ve been perplexed for a week. You’ve been patiently waiting for me to read my bathroom scale on top of my 210 mile high mountain that apparently even the U.S. Geological Survey knows nothing about (I checked at their web site.) Wait! You say you have no clue what I’m talking about?? Hey, you’ve got to read Weekly Challege 4 FIRST! None of this lazy stuff going right to the answer.

Go read Weekly Challenge 4, think about it for a while, and come back. I’ll wait right here for you.

And now the answer—

So I go to the top of my 210 mile (340 km) high mountain, and look … here comes the space shuttle … and there it goes! Man, it was moving fast. It was cruising at a whopping 4.5 miles PER SECOND (7 km/s)! So 2 seconds ago, it was 4.5 miles away heading right for me. A second ago it flew right by my face, and I looked in the window really really fast. And now it’s 4.5 miles away heading away from me.

Sure enough, when I looked inside, the astronauts were weightless—just floating around. So then I looked down at my bathroom scale, also expecting to be weightless—after all I’m at the same place they were. BUT WAIT!! My scale says I weigh nearly the same as my weight in my bathroom at home. More precisely, on top of my mountain I weigh 90% of my weight at sea level! So if I weigh 150 lbs (68 kg) at sea level, I weigh 135 lbs (61.2 kg) on my mountain. Hmmm, wonder if I’ve discovered a new way to diet. (And I bet some of you won’t buy this without seeing the calculations. That’s good. That’s being a great scientist. Keep reading.)

But this can’t be right!  Why are the astronauts weightless?

Lots of folks assume that a weightless astronaut means that gravity is somehow turned off in space. But you don’t need to think about this long to realize that’s a big-time misconception. Gravity is keeping the space shuttle in orbit around the Earth, the Moon in orbit around the Earth, and the Earth in orbit around the Sun. If we suddenly turned gravity off, the Earth would fly out of its orbit, off in a straight line, and head out of the Solar System. Gravity GOOD. No gravity BAD.

First some gravity basics. The force of gravity exists between any two masses, e.g., you and your chair, or your car and the fire hydrant it’s parked next to (hey move your vehicle.) But as forces of nature go it’s a weak force. So for you to easily see it in action, at least one of the masses needs to be really massive. A good example is the force of gravity between YOU and the EARTH. The Earth is pretty massive, and the force exerted on you by the Earth is what we call YOUR WEIGHT. The force between two masses also depends on the distance between them. If you increase the distance between two masses, the force of gravity decreases. This comes together mathematically in the LAW OF UNIVERSAL GRAVITATION, a cool and pretty simple equation courtesy of Mr. Isaac Newton.

Ok, now let’s apply this. In the case of you and Earth, the distance between you and Earth is actually the distance between you and the center of Earth. But that distance is just the radius of Earth, or 3,963 miles (6,378 km.) When I go from sea level to the top of my really tall mountain, 210 miles (340 km) high, I’m increasing the distance between me and the center of Earth only a little bit. So my weight only goes down to 90% of its value at sea level. I actually used Mr. Newton’s equation to calculate my weight on top of my mountain. For those of you that want to see the calculation, I wrote it in my scratchy long-hand HERE.

Here’s another thing to ponder. The space shuttle is pretty massive compared to you, and when it goes into orbit at 210 miles altitude, the space shuttle weighs 90% of its weight at sea level. The weight of an astronaut is also therefore 90% of his/her weight at sea level. THEY ARE NOT WEIGHTLESS. The term WEIGHTLESS leads to a deep misconception. They APPEAR weightless. Big difference. Remember that your weight is the force of gravity exerted on you by the Earth. There is NO question that such a force is exerted by Earth on both the space shuttle and the astronauts inside.

But why do they APPEAR weightless? Well in my case, I’m standing on top of my mountain, where the mountain is holding me up and keeping me from falling under the action of gravity. Gravity is pulling me down with a force defined as my weight, and the mountain is reacting under the ‘load’ with an equal and opposite force up. So for me, I feel two forces: gravity pulling me down, and the mountain pushing me up. The forces cancel, and I just stand there at 90% of my sea level weight. I know that because the spring in my bathroom scale is being compressed between the two forces, and it’s causing the scale to record my weight. My bones also feel the resulting compression, which lets my body know they’re doing a good thing and are useful to keep (not the case in orbit where bone calcium is excreted.) But the space shuttle is not resting on a mountain or anything else. The space shuttle is ONLY experiencing the force of gravity. When that happens we call the situation free fall. The space shuttle is falling!! I know! (says Craig Ferguson.) This seems contrary to the way most of us think about falling objects, where an object that is falling is headed toward the Earth. But that too is a misconception. The space shuttle is falling around the Earth! Here’s something I wrote for a grade 5-8 lesson on free fall (See “To Teachers” section below), and it explains how you can be falling around the Earth.

Now back to the idea of weightlessness. Here is the analogy to help you understand. You’re in an elevator in a tall building. The elevator is on the top floor. Inside the elevator you’re standing on your bathroom scale. You note the scale reads your correct weight plus a couple of pounds ’cause you just finished lunch at the spiffy top floor restaurant. Two forces are acting on you—gravity pulling you down, and thankfully the floor of the elevator pushing you up. Now (sorry) I cut the elevator cable. You feel that in your stomach? You’re now in free fall. You’re falling because I removed the ability of the elevator’s floor to push you back. The floor of the elevator is now falling WITH you. And the bathroom scale between your feet and the floor? Well, it’s also falling WITH you! There is now no way for the spring in the scale to be compressed between your feet and the floor … because the floor isn’t going to be pushing back. Look at the scale … it reads ZERO. You are weightless … look—you’re floating in the elevator.

Ok, just stopped you with the emergency brakes.

So here is the deal. If you are inside something falling (in free fall) like an elevator or space shuttle, you appear weightless. That’s because everything inside is falling with you, including the floor, walls, and ceiling—though calling them floor, walls, and ceiling is now rather meaningless.

A note to the sneaky (those that want to say “but Dr. Jeff you’re wrong.”) Yes, if the object is falling inside the atmosphere (like our elevator), it is technically not in free fall since the drag caused by the air is a real force to be considered. For instance, if you jump out of a plane, you’re not in free fall long. Soon you get up to about 100 mph (160 km/hr) and you won’t go any faster because the force of gravity down is balanced by the drag force up due to the air. But that’s still a bit too fast for a landing, so you open a parachute to dramatically increase the drag from the air, and you live to jump another day.

To teachers:

We developed a great grade 5-8 lesson which easily demonstrates that astronauts inside a free falling soda bottle space shuttle appear weightless. The lesson is part of the Building a Permanent Human Presence in Space compendium of lessons for our Journey through the Universe program. The lesson is titled Grade 5-8 Unit, Lesson 1: Weightlessness, which can be downloaded as a PDF from the Building a Permanent Human Presence in Space page. You can also read an overview of the lesson conducted as part of one of the many Journey through the Universe Educator Workshops, this one in Muncie Indiana.

Contact me if you would like to bring Journey through the Universe to your community, which is programming for hundreds to thousands of grade K-12 students, their teachers, and their families, based on a community-wide engagement model for STEM education. Or you might want to consider just a professional development workshop for educators, or a family and public program, through the Center’s To Earth and Beyond initiative. Here is a list of the family and public program topics with descriptions, which are presentations we routinely conduct after hours at the Smithsonian’s National Air and Space Museum for 450 attendees as part of the Center’s Family Science Night program.

Photo credit: NASA (there was no mountain in their photo—promise.)

This post is a Dr. Jeff’s Weekly Challenge and a Teachable Moment in the News.

As I write, NASA engineers at Kennedy Space Center are working mightily on space shuttle Endeavour to repair a hydrogen leak that scrubbed the June 13, then June 17 launches. Endeavour is headed for the International Space Station. NASA reports that the next flight opportunity is July 11—WHICH MEANS I’ve got plenty of time to get ready for my way cool experiment.

I’ve heard a lot about weightlessness, and astronauts having a great time floating around. The shuttle flies at an altitude of 210 miles (340 km) when rendezvousing with Space Station. (For a cool take on this read my earlier post The Business Trip.) So I wanted to find out first hand what’s going on up there. Since they don’t have a spare seat, I looked far and wide to find an amazingly tall mountain whose peak rises to the shuttle’s orbital altitude. See my mountain in the picture? Mt. Everest is only 5.5 miles (8.8 km) high. MY mountain is 210 miles (340 km) high. It took me some time but I finally found it south of the Land of Make-Believe, down a not too well traveled path. Still, you’d think someone would have noticed it.

While the shuttle is delayed I’m going to take the time to climb my mountain, and in my hand is my trusty bathroom scale, spring-loaded and guaranteed to be accurate at any altitude. I’ll camp out at the top until the shuttle is launched, and I’ll wait until it flies right by my mountain, so I can look in the windows and see them weightless.

Here now the challenge—

As soon as I confirm they’re weightless in the shuttle, I’ll look down at my bathroom scale to see my weight. If I weigh say 150 lbs (68 kg) when I’m standing on my scale in my bathroom at home, what will I weigh on top of my mountain?

Hint: I’m not asking you to actually calculate my weight. I’ll do that (if I need to) in the Solution to the Challenge. Your assignment—if you decide to accept it—is to guess what you think I’ll weigh. Hmmmm, lots of possibilities.

Answer now posted here!

Photo credit: NASA (there was no mountain in their photo—promise.)

Touchdown at Tranquility Base: T-minus

A Footprint on Another World: T-minus

This post is a Teachable Moment in the News.

This is crossposted at the Huffington Post HERE.

We came in peace for all mankind

It was a moment that changed us. A moment that began a new chapter in the book of the human race. It was an achievement shared by all the peoples of the world … and in that moment—our differences were overwhelmed by the common bond of our humanity. And hear ye future generations—it was a testament to what we are collectively capable of achieving when we aim beyond the horizon.

Many of you reading this lived through it and were powerfully moved. Many of you were not yet born—but yearn to know what it was like.

I created this special post as a place where those that lived it could share the experience with those that did not.

If you were moved 40 years ago next month, please leave a comment below. Think about where you were, what it meant to you, and what it meant to the world. And we warmly invite you to put your thoughts to ‘paper’ here.

I’ll start it off with my own very personal experience in the recent post: The Launch of Lunar Reconnaissance Orbiter Brought Back Memories of Apollo 11.

I have also assembled a list of resources below to help you celebrate with friends and family, and follow the flight—in real time—as it happened 40 years ago. I’ll be adding more to the list every few days.

With best wishes for great memories and wonderful sharing time,

Jeff Goldstein, Center Director, NCESSE

Please Tweet and Email the existence of this page far and wide, so we can remember together.

Return often to read new comments below with friends and family.

Feel the magic and the majesty—again.

Resources

Added June 27, 2009:

Blog on the Universe Relevant Resources

Here are some relevant pages I wrote that you can explore and discuss as a family—

•A personal look at the National Mall in Washington, DC, and the National Air and

Space Museum. The page includes a description of the flight of Apollo 11 and the

video of Neil Armstrong placing the first footprint on another world.

• The Nature of our Existence, that speaks to what we know about our place in a

greater space and how we’ve come to know it, and the obligation of each generation

to inspire and teach the next.

• Read the page on Scientists and Engineers as Heroes to get a sense of what we’re

capable of achieving if we work hard and smart.

• On my Favorite Quotes page, read about what poets and explorers have to say about human exploration, and in the last quote by Fred Hoyle, be sure to click on the links for the very first views of Earth from orbit, from the Moon, and from beyond.

• The Resources for Parents page includes ideas for how to use this blog to promote

family discussions on the nature of human exploration, science, and learning; and

at the bottom of the page is a link to a library of Apollo 11 color photographs.

Online Simulation of Apollo 11 Flight in Real Time

Goes live July 16, 2009, 9:32 am EDT, moment of launch

JFK Presidential Library and Museum, powered by AOL

The Press Release

The site: http://www.wechoosethemoon.org/

Features:

• a mission tracking widget for Facebook, Myspace, and your desktop

•a realtime Twitter feed for Mission Control https://twitter.com/AP11_CAPCOM

and for the Apollo 11 spacecraft http://twitter.com/AP11_SPACECRAFT

Apollo 40th Anniversary Website

National Aeronautics and Space Administration

http://www.nasa.gov/mission_pages/apollo/40th/index.html

Smithsonian’s National Air and Space Museum 40th Anniversary Website

Features: interactive Apollo timeline, artifacts, iconic images

http://www.nasm.si.edu/events/apollo11/

Twitter Feed—Apollo 11 As It Happens

Nature News

http://twitter.com/ApolloPlus40

Exploring the Moon

Lunar and Planetary Institute, USRA

http://www.lpi.usra.edu/expmoon/

Features: history of lunar exploration, both robotic and human

Added June 28, 2009:

Apollo 11 Website at Kennedy Space Center

Features: wealth of information on crew, vehicle, and flight milestones.

http://www-pao.ksc.nasa.gov/history/apollo/apollo-11/apollo-11.htm

Project Apollo Image Galleries

National Aeronautics and Space Administration

Features: remarkable, easy to use library of downloadable images and videos

http://spaceflight.nasa.gov/gallery/images/apollo/

Added July 7, 2009:

Moon Landing Factoids

Discovery Channel

http://dsc.discovery.com/space/slideshows/apollo-facts/

Twitter Feed—Apollo 11 As It Happens

Smithsonian’s National Air and Space Museum

http://twitter.com/reliveapollo11

Added July 9, 2009:

National Public Radio Audio Library

I went through NPR’s library dating back to 1997 and found interesting radio shows on the space program and project Apollo. Listen to these with friends and family.

MOON MEMORIES, December 12, 1997

Apollo 11, July 17, 1999

Man Walks On The Moon, July 19, 1999

Apollo Launch, July 20, 1999

Apollo 13 Flight Director Gene Kranz, April 14, 2000

Race to the Moon, May 25, 2001

Remembering Jack Riley, April 23, 2003

Buzz Aldrin: Return to the Moon, December 18, 2003

Apollo 11′s Close Call, July 20, 2004

Timeline: America’s Space Program, July 12, 2005 (not audio but interesting)

Search Is on for Original Apollo 11 Footage, July 31, 2006

Reflections on the Apollo I Disaster, January 28, 2007

Revisiting America’s Fear of Sputnik, October 4, 2007

Biography Chronicles von Braun, ‘Dreamer of Space’, October 26, 2007

Excerpt: ‘Final Countdown’, by Patrick Duggins, November 21, 2007 (not audio but interesting)

40 Years Later, Apollo 8 Moon Mission Still Awes, Dec 24, 2008

Race to the Moon: 5-Part Downloadable Broadcast

Voice of America

Feature: in Special English for listeners not fluent in English

http://www.voanews.com/specialenglish/2009-06-09-voa4.cfm

Apollo Lunar Surface Journal

Features: a one-stop-shop for lots of the NASA flight

http://history.nasa.gov/alsj/

Moonwalk One – The Director’s Cut

Apollo 11 Film Commissioned by NASA

available at Amazon

http://www.moonwalkone.com/

Added July 15:

Apollo 11 Audio Cast in Real Time

National Aeronautics and Space Administration

http://www.nasa.gov/externalflash/apollo11_radio/

Photo credit: NASA

Countdown clocks courtesy of my friend, Drew Roman, Decisive IT.