# Questions tagged [gravity]

Questions regarding the attractive force present between two masses. If about research in artificial gravity (i.e. manmade substitutes for gravity), please use the artificial-gravity tag.

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### What is the formula to calculate how much fuel is needed for a rocket?

I'm theoretically trying to launch a rocket for a school project and therefore I chose Saturn V. I took its weight of 140.000kg (308 647 pounds) and I'm trying to calculate how much fuel it'd take to ...
40 views

### Is the measurement of distance and position of far away objects accurate? [migrated]

Considering that light is affected by gravity, how accurate are our measurements of distant stars and galaxies? When light passes through objects with great mass, such as Jupiter size planets, or ...
2k views

### Can a satellite orbit the ISS?

Is stable orbit of a small satellite around the ISS theoretically possible with minimal station keeping?
148 views

### What is a gravity gradient?

The statement: 'For most of that day, Mir remained in a "gravity gradient," (sic) which basically means that the most massive part of Mir naturally pointed toward Earth.' is in https://...
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### Gravitational potential [closed]

I understand how we calculate gravitational potential and how we set it to be zero at infinity, and I understand its value at he Earth's surface is $-64\,\mathrm{MJ/kg}$ by using $r$ as Earth's radius....
58 views

### Science Contest Topic (space exploration)

I'm thinking of entering the Breakthrough Junior Challenge. It is a global science video contest in which participants have to explain a hard science/math topic in a 3 min video. Right now I'm ...
3k views

### Would an astronaut experience a force during a gravity assist maneuver?

When an astronaut is inside of a ship accelerating (from engine burns), or decelerating (due to reentry) they experience a tug in a relative direction. Suppose an astronaut is in a space ship that is ...
71 views

### Archimedes Principle on other planet [closed]

How does the Archimedes Principle work on other planets where the gravity is different.? Does the wood block will float exactly same in water tub on different planets as on Earth.?
244 views

### What does the Moon's gravity feel like? If you don't move, could you still tell you're on the Moon?

I am interested in descriptions and discussion from the Apollo astronauts. Almost all animals and many plants are sensitive to the earth's gravitational field. This is important for large mammals and ...
130 views

### Gravitational force of asteroid Bennu

How can the gravitational force of Bennu (being so weak) hold the spacecraft in orbit?
207 views

### What keeps galaxies together? [closed]

The super massive black hole at the centre of Milky Way has a mass of about 4 million times that of our sun. Is this enough to keep the entire galaxy together, is it this black hole which keeps the ...
6k views

### Can a smart phone function in space?

I recenty came a across a doubt... Can a smart phone be used in space? Obviously you aren't going to get any data signal, but will the functions like touch screen, GPS, accelerometer, vibrator, etc, ...
168k views

### Couldn't I escape Earth's gravity traveling only 1 mph (0.45 m/s)?

It is said that in order for an object or a projectile to leave Earth's gravitational pull, it must reach Earth's escape velocity, meaning reach a speed of 7 miles per second (~11 km per second). Well,...
30 views

### If I know the masses, positions, and velocities of two objects, how do I calculate their trajectories under gravity?

I was thinking about the effect of a near-miss with an asteroid upon the orbit of the earth around the Sun. My goal is to figure out a formula I could use for a visualization I'd like to build to get ...
285 views

### Can Oberth bike? Is biking up and down a series of hills a good real-world analogy for understanding either the Oberth effect and/or gravity drag?

When faced with a series of ups and downs while riding a bicycle, I try to pedal like mad near the bottoms to gain as much speed as possible. I do this due to some vague, ill-formed notion that either ...
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### Can we destroy an asteroid by spinning it?

In a YouTube video Colonizing the Solar System, part 2: the Outer Solar System, Isaac Arthur who is a YouTuber and also a physicist says something like "you don't spin an asteroid for artificial ...
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### My vector math seems to be off in this 2D simulation of a solar system

I intend to simulate gravitational acceleration on a 2D plane (simplified, no gravitational constant). My code is interpreted without any error in the console, but instead of having the two circles ...
480 views

### Earth geopotential effect on orbit propagation

I'm trying to take into account the Earth geopotential effect on the orbit. The only term I could consider, is J2. Are the terms (J2, etc.) change with time? I ...
112 views

### Two spaceships fly straight, parallel to each other, tied to each other by a rope, and pass a black hole between them. What happens to the rope? [closed]

To elaborate more on what I mean: Two spaceships are flying parallel to each other, both going completely straight relative to the observer. Their distances between each other do not change, as the ...
345 views

### The Earth's Moon versus Phobos and gravity

Our Moon weighs 7.35 x 1022 kg and Mars' moon Phobos, weighs 10.6 × 1015 kg. How much would need to be added to Phobos to give it the same gravitational "impact" on Mars, as the Moon ...
277 views

### Questions about the Dynamic Solid Tide

I found the following plot in the book Satellite Orbits; Models, Methods, Applications by Oliver Montenbruck and Eberhard Gill, Springer, 2000. The figure and description can also be found in google ...
654 views

### Two 1000 kg gold spheres orbit their CM in near-contact, great way to measure G or limited by spaceflight issues?

The hypothetical, non-existent crowdfunding site go-launch-me is so confident, they are offering a two-for-one special. For a limited time, if your project is funded they will foot the bill for a 2nd ...
2k views

### Does trajectory of an object orbiting a planet depend on the object's mass? (With hypothetical Apollo example)

For example (hypothetically), if an Apollo crew of one of the lunar missions went on EVA just after Trans Earth Injection burn and carefully released a small bolt, or a plastic package from their food,...
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### Unix Epoch in International Space Station

The International Space Station is in a different gravitational field than us on the Earth's surface. Almost all computers / protocols depend on the Unix epoch being consistent everywhere. The Unix ...
3k views

### Could magnetic “boots” be used to simulate the effects of gravity for asteroid ships?

I have been to the Wikipedia pages on alternatives to gravity, and found the usual alternative forces, with the potential for magnets and the specious Russian claims, but I'm wondering why not just ...
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### Simple explanation for the 2nd “cosmic speed”

Many sources can explain about the first, second and third cosmic velocities, but the explanations contain difficult formulas and are not easy to understand. I can check with a powerful magnet and an ...
295 views

### How does a rocket go from gravity turn to orbit?

A rocket launch normally begins with a roll to align with the orbital plane and a pitch to allow gravity to gradually torque the rocket down as it climbs. The combined roll and pitchover maneuver last ...
106 views

### Does gravity affect sweating?

I read this hot question. It's asked what is done with the sweat produced by astronauts in the ISS. This led me to question: does gravity affect the production of sweat? Is more, the same, or less ...
3k views

### Time dilation between Mars and Earth due to different mass

I am not sure I understand the Time dilation correctly but if mass has dirrect impact on time...than lets consider cosmological event - one orbit of planet Earth around Sun. This event will person on ...
254 views

### Is Earth's “pear shape” mostly J₃?

@OrganicMarble's answer to 1959 Peanuts cartoon about the Fischer ellipsoid (Earth is “pear-shaped”)? finally let me see the cartoon that Mathematician, Engineer and Geoscientist Irene Fischer wrote ...
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### History of investigation of lunar and Martian surface gravity

I wonder when it was discovered that the Moon has about a sixth of the Earth's surface gravity and that Mars has 0.38 g. I think that until Newton, everyone assumed there was the same gravity on every ...
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### How does gravity vary in a gas giant's interior?

The Earth's gravitational pull in its interior looks like this: The pull remains about the same and increases even a bit till the outer core from where on it starts getting weaker till 0g in the core'...
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### What is the context of this seemingly “zero-gravity” photo on Earth?

A man appears to be in zero gravity in a room which doesn't look like it could possibly be inside of an aircraft. If so, that's one gigantic aircraft, entirely unlike all the other photos of the "...
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### Can you ride a bicycle on Deimos?

Deimos is the small moon of Mars. The surface gravity is 0.003m/s2 (compare to Earth @ 9.807 m/s2). In theory a person with a bicycle could launch from and land on Deimos with a bicycle and a ramp. ...
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### Escaping moons conflict with what I understand of gravity

I have known that the Earth's Moon, let's call it Luna (tip of the hat to The Expanse), has been slowly but surely increasing it's distance from the Earth by a small measure each year. This week I ...
204 views

### Why are all possibly habitable exoplanets higher mass than Earth?

I have been writing a scifi book in which I wanted to include real stars and planets as locations. It was simple enough to find a chart on Wikipedia that lists possibly habitable exoplanets, but I ...
437 views

### At a height of 100 km, what speed do you need to be going to escape Earth's gravity?

I understand that the escape velocity of Earth is 11 km/s. However, Earth's gravitational sphere of influence is not infinite, so it is possible to go slower than that and still escape the sphere of ...
150 views

### Have gravitation multipoles of Jupiter and Saturn beyond J2 been measured or at least estimated? At least the zonal harmonics?

This excellent answer has me wondering if there are any measurements or estimates of gravitational multipole moments of Jupiter or Saturn beyond J2. Here is what I found for J2 (in unitless form) in ...
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### Did any spacecraft ever use the Sun's gravity for acceleration?

Space probes often use planets to accelerate onto a trajectory towards their goal(s) without having to consume too much fuel. But the fastest acceleration would be made through the Sun's gravity if ...
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### How does a planet's gravity push away smaller bodies that would otherwise intersect its orbit?

I was reading an article about dwarf planets online where I stumbled upon the following definition of a planet: The International Astronomical Union defines a planet as being in orbit around the ...
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### If you fell into a crater on the moon in your spacesuit and no jetpack, is there a way to use low gravity to get out of the hole?

If you fell down a crater or hole on the moon, is there a way to exploit microfravity/low gravity to get to the top? Lets say your survived a fall into Aristarchus crater on the moon with a slow slide ...
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### How much gravity could someone handle who lived his/her entire life in microgravity? [closed]

Let's say someone who was conceived and born in microgravity and spent his/her entire life on a space station in weightlessness until age 20 decides to land on a celestial body. How much surface ...
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### How close would the Tesla Roadster with Starman have to get to Earth in order to become attracted and fall on Earth?

In 2091 the Tesla Roadster is said to maybe get closer to Earth than the Moon is. At Starman's current speed, would its location in 2091 be sufficient for the Earth to re-attract the Starman to let it ...
335 views

### Lambert problem solver needed for custom gravity in Python

I need to solve the Lambert problem, however, I have a custom gravity model. My ODE of motion is: ...
32k views

### Do the planets really orbit the Sun?

We often say that the planets orbit the Sun, which is usually a reasonable approximation. But in reality both Sun and the planets orbit the center-of-mass/center-of-gravity of the whole solar system, ...
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### Is it possible for a moon to have a higher surface gravity than the planet it is attached to?

Is it possible that a moon has a higher surface gravity than its planet? I guess it would mean that the moon has a higher mass, but then it would be the planet gravitating around the moon and the ...
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### What counts as “0 mGal” in these gravity maps?

In the following gravity map of Mars the changes in gravity are shown according to mass distribution: Map removed However, since no moon or planet other than the Earth with 9.80665 m/s² has a ...
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### How much does it cost to land on a lunar mascon?

This answer to Delta-v for landing on the moon estimates that to go from a circular orbit at 110km to a landing on a spherical Moon would require an absolute minimum of 1736 m/s and the Apollo landers ...