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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146 votes
12 answers
178k 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,...
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127 votes
4 answers
33k 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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51 votes
6 answers
15k views

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 ...
42 votes
3 answers
10k views

Have we attempted to experimentally confirm gravitational time dilation?

Mark Adler wrote in an answer to a different question that We would expect that Voyager 1's local time is faster than Earth time by about one part in one hundred million. I don't think that ...
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39 votes
1 answer
6k views

Does it require less energy to reach the Sun from Pluto's orbit than from Earth's orbit?

Somewhat inspired by this question and its answers, does it require less delta-v for an object to fall into the Sun the further away it is from the Sun? It makes sense that an object has to shed its ...
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38 votes
2 answers
6k views

Could weights make walking on the Moon feel like walking on Earth?

The Moon has about 1/6th of Earth's gravity, which (it is said) would perhaps lead to muscle degeneration for humans living there long-term. However, what if those humans wore bodysuits weighted to ...
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36 votes
7 answers
9k views

How much stronger does gravity have to be for space travel to be impossible? [duplicate]

I’ve heard that only a slightly stronger gravitational pull would make it impossible for rockets to launch. Is this true? I’ve heard this used as the reason why humanity is meant to be in space.
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34 votes
3 answers
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What causes microgravity (i.e. non-zero gravity) in orbit?

NASA and others seem careful to talk about microgravity instead of zero gravity. Why is for example the ISS not in zero gravity? Is it because of movements onboard? Because of variations in center of ...
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27 votes
4 answers
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Why did Voyager 2's velocity drop far below escape velocity before the first gravity assist?

As per @kasperd's comment on another question. Looking at the graph below, it appears that Voyager 2 started at just over escape velocity of the solar system. Just before the Jupiter flyby, it was ...
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26 votes
7 answers
19k views

Could a Human reach escape velocity by jumping from the surface of Ceres (a dwarf planet)?

According to this answer the surface gravity of Ceres is estimated to be only $0.27 m/s^2$. With a rotation period of 9 hours. The gravity seems light enough to overcome by leg muscle alone, and if ...
25 votes
5 answers
16k views

If human space travel is limited by the G force vulnerability, is there a way to counter G forces?

I read somewhere that prolonged G forces (even 2 Gs) are not tolerated by human physiology and that this ultimately limits our ability to sustain space travel. Are there any tactics to reduce G force ...
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25 votes
3 answers
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What is the "mass" of a Lagrange point?

Of the five Lagrange points, L4 and L5, as stable points, can be orbited by asteroids, satellites, and any other useful or interesting object. Assuming two-body motion however, calculating orbits with ...
24 votes
4 answers
6k views

Is there a self-rounding celestial body from which an Olympian could jump into space?

Is there a self-rounding object in our solar system whose mass is insufficient to prevent the highest jumping human from escaping its gravity?
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24 votes
0 answers
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Why is artificial gravity not included on space stations? [duplicate]

I'm wondering why artificial gravity is not included on the ISS, or on the currently planned OPSEK. There are long-term health effects of weightlessness, which would be avoided, using artificial ...
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23 votes
7 answers
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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 ...
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22 votes
1 answer
3k views

How did the Apollo astronauts train for the 1/6G lunar landing?

It goes without saying that training/conditioning one's reflexes for a situation is highly relevant to some professions. Pilots train in a computer simulator. During the Apollo missions computers ...
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21 votes
2 answers
11k views

Could colonizing Moon dangerously affect its gravity?

If we colonized Moon it would mean we are moving matter from Earth to Moon. Since Moon is much smaller than Earth could these changes somehow affect its trajectory/movement to the point we could ...
20 votes
2 answers
3k views

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 ...
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20 votes
2 answers
3k views

How fast could a person run on the Moon?

Measures of the vertical and horizontal vectors of athletes running shows that once they get up to speed the ratio of vertical to horizontal exertion is about 4:1. This paper by Jean-Benoit Morin Ph.D....
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19 votes
6 answers
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How can astronauts float in space without being affected by the gravitational force of nearby objects?

According to the Newton's law of universal gravitation: Any two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely ...
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19 votes
2 answers
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Why does Voyager 1 lose speed after the sudden gain in speed from gravity assist?

The Voyager 1 loses speed gradually after gaining speed from gravity assist. Is the external thrust is applied in the opposite direction to move closer to the planet, or does the spacecraft lose its ...
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19 votes
3 answers
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Did the Mars rovers actually confirm the gravity of Mars?

For years the theoretical calculated gravity of Mars has proliferated science texts and Internet documentation - but did the rover actually do a test to confirm the theoretical gravity is truly equal ...
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19 votes
3 answers
7k views

Does lower gravity on Mars make it unsafe and unhealthy for humans?

I've been thinking about proposals to live on Mars. One idea is to create an artificial magnetic field to protect from solar radiation. Another idea is to warm the planet using solar mirrors. In the ...
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19 votes
1 answer
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Would my weight be constant on Pluto?

Since Pluto and Charon have distinct orbits around their barycenter (located approximately 960 km above Pluto's surface), the centripedal acceleration must be different on the outer hemisphere of ...
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19 votes
2 answers
3k views

How deep is the force well of L4 and L5 Lagrangian Points of Earth-Sun set?

The Lagrangian Points are points in space, where the combination of gravitational pull of a set of two bodies and the centripetal force of orbiting one of them add up to zero. The special property of $...
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18 votes
7 answers
8k views

Is the zero gravity experienced in ISS the "artificial" kind?

I always wondered about the following: An astronaut floating inside a spaceship that is far from Earth or any other other planet will experience true zero gravity because there is negligible ...
18 votes
2 answers
7k views

Is Mars' gravity strong enough to hold a human-breathable atmosphere?

If we ever try to make Mars outdoors habitable, won't the air just keep flying off into the outer space because of low gravity?
18 votes
2 answers
3k views

Are there any videos of onboard the Apollo Lunar Module while landed on the Moon?

These would be very worthy videos since there is air in the Lunar Module and they don't wear the heavy spacesuits, so one could see how they behave on the Moon in a breathable atmosphere and without ...
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18 votes
2 answers
4k views

Is it possible for a human to walk on an asteroid?

"We’ll start by sending astronauts to an asteroid for the first time in history" (President Barack Obama on Space Exploration in the 21st Century".) With a very low gravity, an asteroid is not ...
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17 votes
11 answers
14k views

If a spaceship ran out of fuel somewhere in space between Earth and Mars, does it slowly drift off to the Sun?

Pretty much what the title is saying. I feel like I am missing something fundamental here and this is driving me crazy. Does a spaceship which is out of Earth's gravity drift to the Sun eventually?
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17 votes
1 answer
546 views

Is GR required to send a probe to Mercury?

I understand that Newton's Law of Gravitation is still used today to calculate the paths of probes, since it is such an accurate theory. However, the Law of Gravitation does not accurately describe ...
16 votes
1 answer
5k views

Can you take a bath on Mars?

A common picture of someone floating on the Dead Sea or Great Salt Lake, shows how high you float. l If you had that water in a bath tub, I don't think you would sink to the bottom, you would just ...
16 votes
3 answers
3k views

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 ...
16 votes
2 answers
566 views

How large could Hyperion be and stay porous?

Here is a question originating on the Worldbuilding stack. Hyperion is porous, with a density of 0.55 g/cc; a little more than half that of water. from https://www.space.com/20770-hyperion-moon.html ...
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15 votes
2 answers
5k views

How does a space probe maintain its trajectory while passing through the extreme gravitational field of the gas giants of our solar system?

Space probes like Voyager 1, 2, New Horizons, etc, traveled beyond those gas giants, how did they cope up with their extreme gravity? How was the trajectory of these probes unhindered by the immense ...
15 votes
2 answers
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 ...
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15 votes
4 answers
4k views

How is lower/no gravity simulated on a planet with gravity, without leaving the surface?

I have seen videos of simulated lower gravity (possibly for training astronauts). I am curious what methods/techniques can be used to simulate lower gravity like environments without leaving the ...
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15 votes
1 answer
3k views

How many satellites can stay in a Lagrange point?

Lagrange points as I understand it are points in space between 2 objects where the gravitational pull between them is effectively equal. That makes station keeping at these points relatively easy. ...
15 votes
1 answer
3k views

Why is momentum transferred to the moon?

The moon whizzes around the Earth, dragging water after it and producing tides. In a comment on this question, I asserted this would sap the momentum of the moon causing it to fall to Earth. This was ...
15 votes
4 answers
7k views

Max g survivable suspended in water?

With something like a coil gun mass driver in mind where the more acceleration the cheaper the design in mind: If you were to suspend the astronauts in a shallow layer of water and horizontally ...
14 votes
2 answers
7k views

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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14 votes
4 answers
1k views

How do spacecraft measure onboard gravity?

How do spacecraft measure onboard (micro)gravity at any given point in time (especially when subject to the gravitational fields of multiple bodies)? I'm guessing that rudimentary accelerometers won't ...
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14 votes
1 answer
4k views

How does the gravity of a massive non-spherical object act on things around it?

Firstly, not sure if this question ought to be in the physics SE site. Please let me know if it should. Secondly, I don't know a whole lot about physics (I'm just inquisitive). So please try to keep ...
14 votes
1 answer
303 views

At what surface gravity can't astronauts do full steps anymore?

We know that on the Moon in ~1/6 g the Apollo astronauts couldn't make full steps because they jumped with each step. At what surface gravity could you walk more like on Earth and at what gravity ...
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13 votes
2 answers
2k views

Alcubierre "warp" drive and gravitation/orbital considerations

There are a few questions regarding the Alcubierre drive here, so I'll pose this one and see what I get. Currently, our space exploration vehicles, both manned and unmanned, are at the mercy of ...
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13 votes
1 answer
2k views

Would human "superpowers" in low gravity fade away through reduced muscle mass?

If suddenly put in a low gravity as on the Moon or on Mars, humans should feel very strong, easily breaking some olympic records for example. Apollo astronauts have said that they did not get tired ...
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12 votes
3 answers
6k views

Does Virgin Galactic experience real weightlessness?

Does Virgin Galatic go into space high enough to experience real weightlessness? A CNBC article states it's more microgravity centrifugal: The spacecraft essentially does a slow back flip at the edge ...
12 votes
4 answers
5k views

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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12 votes
3 answers
2k views

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. ...
12 votes
4 answers
6k views

Accelerometer in space

If my understanding of the General Theory of Relativity is correct, according to the Equivalence Principle, forces due to gravity and acceleration are indistinguishable. If that's the case, then an ...

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