Weightless?

The Earth's richest billionaires use some of their extra money to go on joy-rides into space. At least to of them have already done so; Richard Branson and Jeff Bezos have visited the border between the planet and space, some 50 miles above the surface. And they've, for a few seconds, escaped the planet's gravitational force and experienced what it feels like to be weightless...

Some of you have already seen the grave errors contained in the above introduction: these billionaires didn't visit space, they didn't escape Earth's gravity, and they've not been weightless, not even for a second. Some of the assumptions we make about the facts of life and the facts about the world are simply wrong. When you go on a diet to loose weight, what you actually try to achieve is to lose mass; you literally want there to be less of you, you try to shed molecules and atoms. How much there is of something, the amount of molecules and atoms, is what we call "mass," and "weight" is the amount of force exercised on that mass by gravity. This gravitational force increases when you're nearer to the planet's core; if you want to lose weight, you could just move to some place high up a mountain. You'll lose just a teeny-tiny bit of weight, but still...

Of course, climbing up to your new house every day would also increase your chances to lose some mass, which is what the real goal is here; you lose mass by burning more calories than you take in, thereby reducing the amount of atoms that make up your body. Here's another widely spread misconception about the basic physics we deal with every day: if something is light, it doesn't necessarily float on water. The buoyancy of objects animate and inanimate is controlled by its "density"; weight, mass and density are often used wrong. Density is mass divided by volume, often denoted as grams per cubic centimetre in the metric system. That's why heavy metal ships can float on water; the inside of the hull is mostly air, and when you calculate the density of the entire thing, you get something that's less than 1 gram per cubic centimetre, which is the density of water. The composition of the entire planet is a function of density as well; The Earth's core is made up of very dense metals, mostly iron, with the inner core being solid and the outer core liquid. Then comes the mantle, which is less dense, and the outer layer is the crust which is the least dense and makes up less than 1% of Earth mass.

So, in our quest to lose weight (not mass!) we just have to travel further and further away from the planet, until we escape completely from Earth's gravity and become weightless, right? Well... not exactly. Although the gravitational force becomes weaker, you never escape it completely. I mean, the Moon orbits the Earth because it's bound by Earth's gravity. The Earth orbits the Sun because it's bound by its gravity. There's no escaping gravity. So why are astronauts, and our billionaire astronaut-wannabees, weightless in space? Well, first of all, the most commonly used altitude for space is 100 kilometre or 62 miles, and I know Branson didn't make it to more than 53 miles. Bezos's Blue Origin only just broke the space-barrier with just over 65 miles. So why did they still experience weightlessness? For the same reason why anyone experiences it in freefall. What we call "weightless" is in fact freefall. The only reason why objects keep floating above the Earth's surface, is because they move sideways really fast. They keep falling towards the planet while their sideways motion keeps them from ever coming nearer to its surface; the net result is an orbit. The International space station and the Moon are constantly falling while their sideways motion keeps them in their orbit around the planet...

Linked below is a short video that explains the concept of "weightlessness" better than I can. And it also gives a good visual representation of how close to the planet our spacefaring friends remain, and how far, in comparison, the Moon is. Just imagine how astronomically far Mars must be, and how ambitious the plans of that other spacefaring billionaire are... I hope you forgive me for repeating some classes I'm sure a lot of you already had in school; I was recently reminded about the freefall-weightlessness connection, something I completely forgot about. I must be getting old...

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