The strange phenomenon of an ordinary nut was once regarded as a secret that could destroy the world, and Soviet scientists hid this secret for more than a decade.
We know that the Earth is like a giant gyroscope in space, rotating from west to east for billions of years. If the North Pole and the South Pole suddenly turn each other by 180° while the Earth rotates, what impact will it have on the Earth? Will human civilization be destroyed?
It all starts with an ordinary nut on the Salyut VII space station.
The missing Salyut VII space station
On February 11, 1985, the former Soviet space station Salyut VII, more than 400 kilometers from Earth, was empty, waiting quietly for the next batch of astronauts to arrive.
It was also on this day that ground crews received feedback on the failure of the Salyut VII electronic system and the station's main radio transmitter was shut down. After analyzing the feedback from the space station, ground crews suspected that the accident was caused by the trip.
Since it is a trip, it is good to restart. After the local commander issued a restart command to the Salyut VII space station, the space station did not react at all.
To make matters worse, five hours later, the ground was completely lost to the Salyut VII space station, a behemoth weighing more than 20 tons, like a kite with a broken line.
No one knows what will happen to it after the loss of contact, and the posture is out of control? Off track? Or smashed into a corner of the globe? If you fall on the surface of the sea or in the wilderness, it is okay, but if you fall in the city, it is not as simple as an accident.
To save the missing Salyut 7, the Soviets had only one way – to send astronauts up for repairs. The heavy lifting ultimately fell to astronaut Janibekov and accompanying engineer Victor Savinikh.
An ordinary nut inside the space station has raised concerns among scientists in the former Soviet Union
This is destined to be a difficult rescue operation, after all, the space station is now "deaf and dumb", and how the spacecraft on which the two astronauts are riding docks with the space station is a big problem.
Under a series of thrilling operations, the two astronauts finally entered the Salyut VII space station and completely controlled the big guy.
Just as Janibekov was turning on the supplies sent from Earth, he noticed a strange scene.
The supply on Earth is locked by a butterfly-shaped nut, which does not remain in its original rotation when the nut falls off. Instead, while maintaining the direction of rotation, the head and tail made a 180° flip, and after a few seconds, it turned back again, and flipped around at regular intervals. (See the picture below for details)
At the time, this was an absolute counterintuitive phenomenon. When Janibekov informed the ground of the situation, it frightened soviet scientists.
You know, our earth in space is equivalent to this nut, the nut will flip 180 ° without external force, is our earth also flipped 180 °?
If the earth were to rotate in the process of rotation and the north and south poles would suddenly rotate by 180 degrees, would the world be destroyed?
Before figuring out the problem, Soviet scientists planned to hide this secret.
A small tennis racket finally solves the puzzle
Six years later, in 1991, a paper called "Twisted Tennis Rackets" was published in academic weekly, and although it did not mention the strange nut that Janibekov found on the space station, the content was the same.
When people hold the handle of a tennis racket with their hands, make one of the net surfaces (A-side) parallel to the ground and turn upwards, and then forcefully throw the tennis racket into the air. The tennis racket rotates in the air for a week, and when one re-grasps the handle, one finds that the A side of the tennis racket will face down instead of upwards.
This phenomenon occurs because the angular velocity component generated by the axis of rotation around the axis of rotation is unstable when the tennis racket is rotated.
We divide the tennis racket into three main axes, axis 1 runs through the entire tennis racket from beginning to end, on the same plane as the racket; axis 2 is perpendicular to the tennis racket and on one plane with the tennis racket; axis 3 is perpendicular to the tennis racket, perpendicular to the face on which the racket is located.
The angular velocity component produced by the tennis racket when rotating around axis 1 and axis 3 is almost negligible, and the angular velocity component increases when rotating around axis 2.
As a result, when the tennis racket rotates around different spindles, the first spindle with the greatest moment of inertia or the third spindle with the smallest moment of inertia is stable. It is unstable when rotating around the second spindle.
This can happen not only with tennis rackets, but also mobile phones, books, remote controls, etc., throwing any object with three different spindles of moment of inertia into the air.
This phenomenon is known by scientists as the tennis racket theorem, or Janibekov's theorem. From this, scientists understand why an ordinary nut has a 180° rotation of the head and tail.
Will there be a 180° reversal during the earth's re-rotation?
In fact, this phenomenon only occurs on rigid objects, and for a non-rigid object, this does not occur.
For example, a bottle containing liquid, when rotating around the axis with the smallest moment of inertia, due to the relative position of the internal particles, the bottle will be displaced, resulting in centrifugal action on both sides of the shaft due to uneven quality. As a result, the bottle will eventually rotate steadily around the axis with the greatest moment of inertia.
Our planet is like this bottle of liquid. Because the earth's shaped poles are slightly flattened and slightly bulging in the middle, the earth dissipates energy internally as it rotates, and over time, it rotates around the axis with the greatest moment of inertia, so it can remain stable.
In fact, not only the Earth, but most of the celestial bodies in space are like this.
In the case of Mars, most of the mass of Mars is concentrated near the Martian equator, so that the mass can be the farthest away from the axis of rotation of Mars, and the stable rotation of Mars around the axis of the greatest moment of inertia.
Say at the end
An ordinary butterfly-shaped nut actually caused scientists to worry about the earth.
For now, we may think that this concern is superfluous. At that time, this phenomenon attracted the attention of scientists, because the scientific concept at that time could not explain why the nut would flip 180 ° on its own without external force.
It is also the exploration of the unknown by scientists that makes our human technological level continue to progress.