Whenever we write stuff and post it on the Internet, it pays to remember that we never know who may end up reading it. I’ve been writing these articles since January 2003.

 

While I write about many topics, my true love remains science—astrophysics in particular. But, I’m no slouch when it comes to exobiology, either. I’ve taught tons of physics courses at the post-secondary level since the early ‘70s.

 

I’m not sharing this with you because I’m looking for “attaboys,” but rather to add context concerning an email I received yesterday, March 7, from a 13-year-old eighth-grade student.

 

She’s been trying to write an essay on why astronauts “float” inside the space shuttle as it orbits Earth. She assumed, according to what she’s heard, that it was due to “weightlessness” in space.

 

But, being a good student, she looked up the name of a physics professor at a local university and emailed him for some information.

 

He wrote back; “Monica, there is no such thing as weightlessness. Space shuttle astronauts ‘float’ around inside the space shuttle because they, AND the shuttle, are in a constant state of free-fall.” He included this link as a detailed explanation.

 

I don’t know this professor, so I’m giving him the benefit of the doubt. I’m sure he was being sincere. Like many university professors, perhaps he was up to his ears writing grant proposals trying to maintain his tenured status and his job.

 

If you click on the above link, your reaction will probably be similar to that of every other normal, sane, adult scientific neophyte: “Holy crap! What the dickens does this mean?” Or, perhaps your first choice of terms would not be “crap” or “dickens.”

 

Monica is only 13-years old. She’s not writing a doctoral dissertation. There is a simpler way to explain this to her.

 

The point of good science is discovery through questions. Sometimes we find immediate answers. At other times, NOT. And, like it or not, we may NEVER find the answers to SOME of our questions.

 

But this is NOT an excuse for us to stop searching, though. But, even if we do find good answers, they’re meaningless if good, solid people of average intelligence can’t understand what science is saying.

 

So, Monica, I’m sure the professor meant well, but here is a simpler answer. I hope it helps you. And, I hope others with similar curiosities will also find it useful.

 

How much we weigh on Earth depends on the force with which gravity pulls us toward the Earth’s center. The average radius of this planet (the distance from its center to its surface) is 3,963 miles. But we’ll round this to 4,000 miles to keep the math simpler.

 

If we move our bodies twice as far from Earth’s center, we’ll weigh only one-fourth (1/4^th) as much. If we move ten times farther away, we’ll weigh only one-hundredth (1/100^th) as much.

 

This is what the professor’s link means. And, we don’t need that complicated formula to explain it, either. We can use a much simpler one: 1/r². Here’s why.

 

Astrophysicists call this radius (from Earth’s center to Earth’s surface) 1-gravity. If you move out into space another 4,000 miles, you’re at 2-gravity.

 

Each time we add an additional 4,000 miles above Earth’s surface, we add one to the number of gravities. The sequence goes 1-gravity, 2-gravity, 3-gravity, etc.

 

Let’s say you weigh 150-pounds according to your bathroom scale. Since you are standing on Earth’s surface, this represents your 1-gravity weight.

 

But, if you hop aboard a space ship and fly out to, say, 4,000 miles above the Earth, you will be at 2-gravity (4,000 miles from Earth’s center to Earth’s surface plus another 4,000 miles ABOVE Earth’s surface).

 

Let’s apply our formula: 1/r². But, instead of using 4,000 miles for “r,” just use the gravity value (1-gravity, or 2-graivity, etc.)

 

At 1-gravity, our formula becomes 1/1². One-squared is ONE. So, at the surface of Earth, your weight is 150-pounds. But at 4,000 miles above Earth’s surface, you’re at 2-gravity.

 

Our formula becomes 1/2². Two-squared equals four (4) and 1 divided by 4 equals 0.25. Your weight is only one-fourth (1/4^th) as much or 37.5-pounds.

 

You can do this for any value of gravity. If you were at 10-gravity, the formula would read 1/10², and you would weigh only one-hundredth as much: 1.5-pounds (1 divided by ten-squared equals 0.01).

 

But, the space shuttle does not orbit at 2-gravity (4,000 miles above Earth’s surface). It only goes up about 180-miles. So, the shuttle astronauts are not at 2-gravity; they’re at 1-gravity plus some percentage of 2-gravity.

 

Which percentage? Simply divide 180-miles by 4,000 miles, and you’ll get 0.045 (4.5%). So “r” becomes 1.045 (1-gravity plus 4.5% of 2-gravity, and, 1/r² becomes 1/1.045², which equals 0.9157. We’ll round it to 0.92 or 92%.

 

In other words, your 150-pound Earth weight would amount to only 138-pounds (150-pounds times 0.92) aboard a space shuttle orbiting 180-miles above the Earth.

 

The astronauts are NOT weightless. But, they ARE “floating” around inside that space shuttle. We see it happen through TV coverage. If it isn’t due to weightlessness, what IS the cause?

 

Astrophysicists call it “free-fall.” This occurs whenever there are no opposing forces that prevent you from falling according to gravity’s law. It means that the shuttle and everything inside of it are “freely” under the influence of gravity.

 

It works like this. If I could put you inside of a baseball and drop it off the top of the Sears Tower, it, with you inside, would fall straight to the ground below.

 

But, beyond the first second of the fall, you would have no sensation of falling because you and the ball would be falling at the same time. You’d actually “float” inside the ball, at least until it hit the ground. Then… EWWWW!

 

Now, instead of dropping the baseball, I threw it as hard as I could away from the building. It would first rise, level off, and then begin to fall back toward the ground.

 

The ball, with you inside, would be following a curved trajectory. However, beyond the initial thrust of my throw, you would have no sensation of movement, up, parallel, or downward.

 

Once again, the ball, with you inside, would be “freely” under the influence of gravity… free-fall, until you hit the ground.

 

Now imagine that I have the strength to throw the ball, with you inside, in excess of 17,000 miles per hour. The ball would still follow the same kind of curved trajectory.

 

Only, now it would be so far out there that it would literally be able to go over the distant horizon.

 

And, because of the throw’s speed, it would continue to go beyond the horizon. It would be following a trajectory of the Earth’s curvature.

 

The ball would still fall downward, but it would never hit the ground because it would be in ORBIT around the Earth. It would continue following the curvature of the Earth, repeatedly, until it some opposing force slowed it down.

 

You would have no sensation of falling or moving at all. You’d be “floating” inside the ball. You would not hear anything outside of the ball’s interior because there is no sound in the vacuum of outer space.

 

So, the astronauts “float,” along with everything else not anchored down, because the whole shebang is “freely” under the influence of gravity.

 

On the other hand, if the astronauts slowed the shuttle’s speed, the curved trajectory would steepen and the whole kit and caboodle would fall back to Earth.

 

But, even as this happened, the astronauts would not feel like they were falling until after they reentered Earth’s atmosphere, where, once again, they’d be able to hear those nasty old frictional noises.

 

Joe Walther is a freelance writer and publisher of The True Facts. You may comment on his column by clicking here.