М.Двач / Космос и астрономия

There are no such thing as Zero G 17 июля, 21:39 812106 В конец треда | Веб

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>at what altitute gravitation starts becoming weaker?

Gravity actually starts becoming weaker as soon as you increase your distance from the center of the Earth. It's a continuous decrease, not something that suddenly "switches off" at a certain altitude.

Here's why:

Inverse Square Law: The force of gravity follows an inverse square law. This means that the gravitational force between two objects is inversely proportional to the square of the distance between their centers. In simpler terms, if you double the distance, the gravitational force becomes one-quarter as strong.

Earth's Center of Mass: For calculations involving gravity, we consider the Earth's entire mass to be concentrated at its center. So, as you go higher in altitude, you are simply increasing your distance from this central point, and therefore, the gravitational pull weakens.

Practical Examples:

Even at the top of a mountain (e.g., Mount Everest), gravity is slightly weaker than at sea level. The change is very small, but it is measurable.

The International Space Station (ISS) orbits at an altitude of about 400 kilometers (250 miles). At this height, gravity is still nearly 90% as strong as at the Earth's surface. Astronauts feel "weightless" not because there's no gravity, but because they are in a constant state of freefall around the Earth.

So, to directly answer your question, gravity starts becoming weaker immediately as you gain any altitude above the Earth's surface. The effect is subtle at lower altitudes but becomes more pronounced the further you travel into space.

>bullshit

I understand your skepticism! It might seem counterintuitive, as we often associate space with a complete absence of gravity. However, the concept of gravity's gradual weakening with distance is a fundamental principle of physics, described by Isaac Newton's Law of Universal Gravitation.

Let me try to explain it in a different way, perhaps with an analogy:

Imagine you have a very strong magnet. The magnetic force is strongest right next to it, right? But even a little bit away, you can still feel a pull, even if it's weaker. The further you move away, the less you feel the pull, but it never completely disappears unless you're infinitely far away.

Gravity works similarly. The Earth is like that giant magnet. Its gravitational pull is strongest at its surface (our "sea level" reference). As you move away from the surface, whether it's up a hill, in an airplane, or into space, you are simply increasing your distance from the center of the Earth's mass. Because of the inverse square law, this increased distance means the gravitational force becomes progressively weaker, but it never truly becomes zero.

Why Do Astronauts Seem Weightless Then?

This is where the confusion often lies. Astronauts on the International Space Station (ISS) aren't in a place with no gravity. In fact, at the ISS's altitude (about 250 miles or 400 km), gravity is still about 90% as strong as it is on Earth's surface!

The reason they appear to float is because they are in a constant state of freefall around the Earth. Think of it like this: if you jump off a diving board, you feel weightless for a moment as you fall. The ISS and everything in it is continuously "falling" around the Earth, but because they also have tremendous horizontal velocity, they keep missing the Earth and stay in orbit. This continuous falling motion creates the sensation of weightlessness.

I hope this helps clarify why gravity doesn't just "turn off" at a certain altitude, but rather weakens gradually with distance. Does this make more sense?

>still sounds like bullshit. how come i never knew that part about ppl on the iss having 90% rate gravity influence?

You've hit upon one of the most common and persistent misconceptions about space and gravity! It's absolutely true that many, many people believe there's "no gravity in space" or that astronauts are beyond its influence. This belief is so widespread for a few key reasons:

Visuals are Deceiving: When we see astronauts floating effortlessly, it looks like there's no gravity. Our everyday experience on Earth teaches us that if something isn't pulled down, gravity must not be there. The "floating" is actually the sensation of weightlessness caused by freefall, but visually, it's hard to distinguish from a true absence of gravity.

Simplified Language: Terms like "zero-G" are frequently used in popular culture, media, and even sometimes in simplified educational materials. While "microgravity" or "effective zero-G" are more accurate (referring to the sensation of weightlessness, not the absence of gravity), the shorthand "zero-G" leads to the misunderstanding.

Intuition vs. Physics: Our intuition is built on our experience with gravity on Earth. We don't often consider what happens when you're constantly falling sideways at thousands of miles per hour. The idea of "falling around the Earth" rather than "falling to the Earth" is a leap for many.

Focus on Escape Velocity: When we talk about rockets, we often hear about "escaping Earth's gravity." This can be misinterpreted as meaning gravity ends at a certain point. What it actually means is reaching a speed sufficient to overcome the pull of gravity and not fall back down, allowing an object to travel further into space or enter orbit.

Let's break down the 90% figure for the ISS:

The Earth's radius is about 6,371 kilometers (about 3,959 miles).

The International Space Station (ISS) orbits at an average altitude of about 400 kilometers (about 250 miles) above the Earth's surface.

So, the ISS is approximately 6,371 km + 400 km = 6,771 kilometers from the center of the Earth.

Now, recall the inverse square law: gravitational force is proportional to 1/r2, where r is the distance from the center of mass.

Let gE be gravity at Earth's surface and gISS be gravity at the ISS:

gE∝1/(6371 km)2
gISS∝1/(6771 km)2

To find the ratio of gravity at the ISS to gravity at the surface:

gISS/gE=(1/(6771)2)/(1/(6371)2)=(6371/6771)2
gISS/gE≈(0.9409)2≈0.885

So, the gravitational force at the ISS altitude is indeed about 88.5% (often rounded to 90%) of what it is on the Earth's surface.

The "Aha!" moment often comes with the "freefall" explanation:

Imagine you're in an elevator, and the cable suddenly snaps. For the brief time you're falling, you'd feel weightless, even though gravity is still pulling you down. If you held a ball and let go, it wouldn't fall to the floor of the elevator; it would float next to you because both you and the ball are accelerating downwards at the same rate.

The ISS and everything in it (astronauts, tools, food, water) are constantly "falling" around the Earth. Because they are moving incredibly fast horizontally (about 17,500 miles per hour or 28,000 km/h), as they fall, the Earth's surface curves away beneath them. They are literally falling around the Earth, continuously missing it, and that's what creates orbit.

Since everything inside the ISS is falling together at the same rate, there's no "floor" pushing up against their feet, and no objects "falling" relative to them. This creates the sensation of weightlessness, even though the Earth's powerful gravitational pull is very much present.

It's a concept that really challenges our everyday understanding, and it's perfectly normal to find it hard to grasp at first!

>motherfuck! thats insane. thanks

You're welcome! I'm glad I could help clarify one of the most surprising facts about space travel. It really is "insane" in the best possible way when you wrap your head around it.

It just goes to show how much more there is to learn about the universe, even in things we think we understand. If you have any more questions or want to dig into other "insane" science facts, just let me know!

vek jivi, vek uchis blyat

2 17 июля, 21:46 2 812107

>so, is the ISS on constant move or is it "standing" on specific coordinates?

The ISS is absolutely not "standing" on specific coordinates. It is in constant, rapid motion.

Here's why and what that means:

Orbiting the Earth: The ISS is continuously orbiting the Earth at an average altitude of about 400 kilometers (250 miles). As we discussed, it's constantly "falling" around the Earth at a tremendous speed.

Incredible Speed: To stay in orbit at that altitude, it needs to travel incredibly fast. The ISS zips around the Earth at approximately 28,000 kilometers per hour (17,500 miles per hour).

Completing an Orbit in ~90 Minutes: Because of this speed, the ISS completes one full orbit of the Earth roughly every 90 to 93 minutes.

Seeing 16 Sunrises/Sunsets Daily: Since it orbits so quickly, astronauts on board experience about 16 sunrises and 16 sunsets every 24 hours.

What does this mean for its "coordinates"?

Because the Earth is also rotating beneath the ISS's orbit, the station's path over the ground shifts with each orbit. It doesn't trace the exact same line over the Earth's surface every time. Instead, its "ground track" looks like a wavy, diagonal line that covers most of the populated areas of the Earth (between about 51.6 degrees North and 51.6 degrees South latitude).

You can actually track the ISS in real-time online! There are many websites (like NASA's "Spot the Station" or other satellite trackers) that show its current position and trajectory. If you watch it for a few minutes, you'll see how quickly it moves across the map.

So, to reiterate: The ISS is definitely a moving target, constantly circling our planet at high speed!

>u mentioned earlier that astronauts on the iss are still under the influence of 80% earth gravity, so how to make them actualy feel it? what if we "stop" the iss moving?

You've hit on a fascinating and crucial point! This is where the physics of orbit really comes into play.

What if we "stop" the ISS moving?

This is a critical thought experiment that reveals why astronauts feel weightless. If you could instantaneously "stop" the ISS's horizontal orbital velocity (that 28,000 km/h or 17,500 mph sideways speed), the astronauts would immediately feel the full force of Earth's gravity at that altitude (around 88-90% of surface gravity).

Here's what would happen:

Immediate Fall: Without the horizontal speed to continuously "miss" the Earth, the ISS and everything in it would immediately begin to fall directly towards the Earth.

Sensation of Weight: As they started falling, astronauts would press against the "floor" of the ISS, just like you feel your weight when you stand on the ground. The floor would be accelerating downwards at the same rate as them due to gravity, but because they are now "stopped" relative to the Earth's center (in terms of horizontal motion), they would be accelerating into the floor of the station.

Atmospheric Re-entry and Burn-up: The ISS is still in a very thin part of Earth's atmosphere (the thermosphere). Without its orbital speed to counteract atmospheric drag, it would quickly lose altitude, encounter denser atmosphere, heat up dramatically due to friction, and eventually burn up or break apart.

Why they feel weightless now (to recap):

It's the constant state of freefall that creates the sensation of weightlessness. Imagine throwing a ball and a feather out of a window at the same time. They both accelerate downwards at the same rate (ignoring air resistance). If you were falling with them, they would appear to "float" next to you. The ISS and everything inside it are doing this on a grand scale around the Earth.

How to make astronauts "feel" gravity in space (Artificial Gravity):

Since you can't rely on being "stopped" relative to Earth in orbit (because you'd just fall), the only practical way to create a sensation of gravity in a spacecraft in deep space or in a stable orbit (where you don't want to fall to a planet) is through acceleration.

There are two main concepts for this:

Rotation (Centripetal Force): This is the most widely discussed and scientifically viable method. If you spin a spacecraft (or a section of it), objects inside will be pushed outwards towards the "floor" due to the centripetal force. This outward push mimics gravity.

Think of a Gravitron ride at an amusement park. You're pressed against the wall as it spins.

For a comfortable amount of artificial gravity (like 1G, Earth's gravity), and to avoid motion sickness, the spacecraft would need to be very large, with a significant radius, and spin at a controlled rate. Sci-fi often depicts large, rotating "wheel" space stations for this reason.

Continuous Acceleration/Deceleration: If a spacecraft were to constantly accelerate in one direction, anything inside would be pushed towards the back of the ship, creating a sensation of gravity. For example, on a long journey to Mars, the ship could accelerate for the first half of the trip, then flip around and decelerate for the second half, providing continuous "down" for the entire journey.

The main challenge here is the immense amount of fuel required for continuous thrust over long distances. Current rocket technology isn't efficient enough for this on a large scale.

So, while the ISS is under significant gravitational influence, the feeling of weight is absent due to its continuous orbital motion (freefall). To bring that feeling back in space, you need to introduce an opposing force, typically through rotation or constant thrust.

2 17 июля, 21:46 2 812107

>so, is the ISS on constant move or is it "standing" on specific coordinates?

The ISS is absolutely not "standing" on specific coordinates. It is in constant, rapid motion.

Here's why and what that means:

Orbiting the Earth: The ISS is continuously orbiting the Earth at an average altitude of about 400 kilometers (250 miles). As we discussed, it's constantly "falling" around the Earth at a tremendous speed.

Incredible Speed: To stay in orbit at that altitude, it needs to travel incredibly fast. The ISS zips around the Earth at approximately 28,000 kilometers per hour (17,500 miles per hour).

Completing an Orbit in ~90 Minutes: Because of this speed, the ISS completes one full orbit of the Earth roughly every 90 to 93 minutes.

Seeing 16 Sunrises/Sunsets Daily: Since it orbits so quickly, astronauts on board experience about 16 sunrises and 16 sunsets every 24 hours.

What does this mean for its "coordinates"?

Because the Earth is also rotating beneath the ISS's orbit, the station's path over the ground shifts with each orbit. It doesn't trace the exact same line over the Earth's surface every time. Instead, its "ground track" looks like a wavy, diagonal line that covers most of the populated areas of the Earth (between about 51.6 degrees North and 51.6 degrees South latitude).

You can actually track the ISS in real-time online! There are many websites (like NASA's "Spot the Station" or other satellite trackers) that show its current position and trajectory. If you watch it for a few minutes, you'll see how quickly it moves across the map.

So, to reiterate: The ISS is definitely a moving target, constantly circling our planet at high speed!

>u mentioned earlier that astronauts on the iss are still under the influence of 80% earth gravity, so how to make them actualy feel it? what if we "stop" the iss moving?

You've hit on a fascinating and crucial point! This is where the physics of orbit really comes into play.

What if we "stop" the ISS moving?

This is a critical thought experiment that reveals why astronauts feel weightless. If you could instantaneously "stop" the ISS's horizontal orbital velocity (that 28,000 km/h or 17,500 mph sideways speed), the astronauts would immediately feel the full force of Earth's gravity at that altitude (around 88-90% of surface gravity).

Here's what would happen:

Immediate Fall: Without the horizontal speed to continuously "miss" the Earth, the ISS and everything in it would immediately begin to fall directly towards the Earth.

Sensation of Weight: As they started falling, astronauts would press against the "floor" of the ISS, just like you feel your weight when you stand on the ground. The floor would be accelerating downwards at the same rate as them due to gravity, but because they are now "stopped" relative to the Earth's center (in terms of horizontal motion), they would be accelerating into the floor of the station.

Atmospheric Re-entry and Burn-up: The ISS is still in a very thin part of Earth's atmosphere (the thermosphere). Without its orbital speed to counteract atmospheric drag, it would quickly lose altitude, encounter denser atmosphere, heat up dramatically due to friction, and eventually burn up or break apart.

Why they feel weightless now (to recap):

It's the constant state of freefall that creates the sensation of weightlessness. Imagine throwing a ball and a feather out of a window at the same time. They both accelerate downwards at the same rate (ignoring air resistance). If you were falling with them, they would appear to "float" next to you. The ISS and everything inside it are doing this on a grand scale around the Earth.

How to make astronauts "feel" gravity in space (Artificial Gravity):

Since you can't rely on being "stopped" relative to Earth in orbit (because you'd just fall), the only practical way to create a sensation of gravity in a spacecraft in deep space or in a stable orbit (where you don't want to fall to a planet) is through acceleration.

There are two main concepts for this:

Rotation (Centripetal Force): This is the most widely discussed and scientifically viable method. If you spin a spacecraft (or a section of it), objects inside will be pushed outwards towards the "floor" due to the centripetal force. This outward push mimics gravity.

Think of a Gravitron ride at an amusement park. You're pressed against the wall as it spins.

For a comfortable amount of artificial gravity (like 1G, Earth's gravity), and to avoid motion sickness, the spacecraft would need to be very large, with a significant radius, and spin at a controlled rate. Sci-fi often depicts large, rotating "wheel" space stations for this reason.

Continuous Acceleration/Deceleration: If a spacecraft were to constantly accelerate in one direction, anything inside would be pushed towards the back of the ship, creating a sensation of gravity. For example, on a long journey to Mars, the ship could accelerate for the first half of the trip, then flip around and decelerate for the second half, providing continuous "down" for the entire journey.

The main challenge here is the immense amount of fuel required for continuous thrust over long distances. Current rocket technology isn't efficient enough for this on a large scale.

So, while the ISS is under significant gravitational influence, the feeling of weight is absent due to its continuous orbital motion (freefall). To bring that feeling back in space, you need to introduce an opposing force, typically through rotation or constant thrust.

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3 17 июля, 21:48 3 812109

я человек далёкий от ваших космических тематик, посему не бейте по хеду сильно за мои дурацкие вопросы, лел

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4 27 мар, 20:28 4 834395

>>812109
Как ребёнок которому надоела игрушка юноша отвёл глаза от смотрового бинокля направленного на огни города вдали от причала Он повернул своё ангельское лицо к мужчине средних лет стоявшему рядомПока они разговаривали лифт наконецто остановился

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5 30 мар, 16:56 5 834514

> ещё один во время школьной физики с этой темой - пил яжку или пиво за углом школы или дрочил в туалете
> vek jivi, vek uchis blyat

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