Never Mind the Bullocks, Here's the Science by Karl Kruszelnicki

Author:Karl Kruszelnicki
Language: eng
Format: mobi, epub
ISBN: 9780730400851
Publisher: HarperCollins Publishers
Published: 2014-07-14T16:49:11.283000+00:00

How Come They Float?

So how come the astronauts float, if they still weigh 90% of their normal weight?

Simple: (1) they are falling because they have weight; but (2) they are moving forward really really quickly; and (3) the Earth is curved, not flat.

Let me explain this to you.

First, the astronauts are so close to the Earth that the Earth’s gravitational field ‘sucks’ on them with 90% of its normal ‘suck’. So they do actually fall towards the Earth. At ground level, if you jumped off a diving board into a pool, you would fall 5 m in the first second. But the Earth’s gravity is a little weaker at their altitude of about 350 km, so they fall 4.5 m in the first second. And yes, they really do fall.

Second, at their altitude, they are also moving forward at about 25,000 kph—in other words, 7 km in each second.

Third, the Earth is not flat—it has the shape of a ball, with a curved surface. At the astronauts’ altitude, the curve of the Earth drops away by roughly 4.5 m for every 7 km that they fly forward.

Therefore in the exact second that they move forward 7 km, gravity pulls them 4.5 m vertically downwards towards the Earth. But (as I said earlier) in the 7 km that they cover in that second, the curve of the Earth is such that the surface of our planet has ‘fallen’ away by 4.5 m.

Free Fall

For our astronauts, the net result is simple. After one second of falling, they are still the same distance from the surface of the Earth.

And so it goes for every single second that they are in orbit at that particular speed and altitude. After 90 minutes, they have made a complete loop of the Earth and are still the same distance from the surface.

In one second, the shuttle moves forward 7 kilometres, while at the same time, gravity pulls it 4.5 metres vertically downwards towards the Earth.

But in the 7 kilometres it covers in that second, the curve of the Earth is such that the surface of our planet has ‘fallen’ away by 4.5 metres.

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