# Gravity in space

1. Feb 22, 2010

### Misr

Hi , people

Life in a space ship
[/QUOTE]

1 -
How come???what does the book mean?gravity does exist in space!! i'm really confused!

2-
If gravity does exist in space why is this true??

3-
also why??

4-
because when the acceleration increases the force acting upon the astronaut increases ??right??

5- If gravity does exist in space so why objects float in space??

6-
so what is the idea of propeller jet chair if its an application to Newton's third law??

Thanks

2. Feb 22, 2010

### Naty1

It must be a unique experience to live without weight in a space ship....everything is normal in a spaceship such as oxygen,pressure but there’s no gravity so :

How come???what does the book mean?gravity does exist in space!! i'm really confused!

THERE IS NO NATURAL AIR NOR PRESSURE EITHER; THAT IS PUT THERE BY THE PEOPLE OR ALIENS WHO COSTRUCTED THE SPACE SHIP.

GRAVITY DOES EXIST EVERYWHERE; BUT IN OPENSPACE WITH LITTLE NEARBY MATTER SUCH AS THE EARTHS MASS, IT IS VERY VERY WEAK. FURTHERMORE, IF YOU ARE FLOATING AROUND IN OUTER SPACE LIKELY YOU ARE IN FREE FALL SUCH AS AN ELEVATOR FREE FALLING TOWARD EARTH...YOU HAVE NO 'WEIGHT'.....SO IT FEELS LIKE YOU ARE NOT IN A GRAVITATIONAL FILED OF ANYKIND....

2-
* You can lift a big man with one finger.
* You can jump up high and stay hanging.
* Plant roots grow upwards due to the absence
of gravity.

If gravity does exist in space why is this true?? SAME AS ABOVE; EXCEPT ROOTS DO NOT GROW "UP", THERE IS NO 'UP'...
AND YOU CAN JUMP UP HIGH BUT IF YOU DO YOU WILL BOUNCE OFF THE CEILING AND BANG YOUR HEAD.

3-
* According to newton’s third law,if you throw
a mass to front ,it pushes you back
with the same force.

4-
*during launching rockets astronauts are under sever or deal(according to newton's second law)

because when the acceleration increases the force acting upon the astronaut increases ??right?? YES AN ACCELERATION IS 'EQUIVALENT' TO A GRAVITATIONAL ATTRACTION ACCORDING TO EINSTEINS EQUIVALENCE PRINCIPLE...NOBODY KNOWS WHY INERTIAL MASS (ASSOCIATED WITH RESISTANCE TO ACCELERATION) AND GRAVITATIONAL MASS (ASSOCIATED WITH GRAVITATIONAL ATTRACTION) ARE EQUALBUT EXPERIMENTS HAVE SHOWN TO A VERY HIGH DEGREE OF PRECISION THAT IS TRUE.

5- If gravity does exist in space so why objects float in space??
BECAUSE THEY ALL FALL TOGETHER, LIKE IN A FREE FALLING ELEVATOR.

6-
Life outside the spaceship:
Astronaut must use the propeller jet chair(which is an application to newton's third law) to move anywhere in the space looking like a satellite.

so what is the idea of propeller jet chair if its an application to Newton's third law??
EVERY ACTION HAS AN EQUAL AND OPPOSITE REACTION....PUSH AGAINST A FRIEND..THAT FRIEND PUSHES BACK AGAINST YOU. LIFT A ROCK..THE ROCK PUSHES BACK AGAINST YOU.

3. Feb 23, 2010

### Raekwon

When people say there is "no gravity" they usually mean it is relatively small compared to what we are used to, it's just a common misconception, poor use of words, the effects of no gravity are the same that the moon for example experiences - it's held in orbit and not pulled to the surface. The moon is held in place by gravity, it's at the position where it's momentum keeps it from being drawn in (the same as the planets) and the gravity keeps it from flying off.

With less gravity, everything has less weight, as weight is defined by how gravity acts on the mass, so lifting a heavy item when there is less gravity is easier as there is less acting against you.

You can jump high because there is less gravity pulling you to a mass it holds you, like the moon, in orbit, hence the apparent floating.

Roots grow towards moisture and nutrients, however gravity has an impact on the way moisture and such is positioned - water drainage etc.

Again, it's like an orbit.

4. Feb 23, 2010

### Rasalhague

Terms like "zero gravity", "microgravity" and "weightlessness" are often used to describe the phenomenon whereby objects don't rest on the "floor" of a spacecraft in orbit as they would on the ground on earth. But these terms, although widely used, are misleading. The strength of the earth's gravitational field is not much less in low-earth orbit than it is on the earth's surface, although it dwindles the further you get into interplanetary space, eventually becoming very slight, although never quite zero.

The important difference between being in orbit and standing on the ground is that the orbiting vehicle is in freefall. This means that it's falling under the influence of gravity.

If a vehicle at that height had no initial velocity relative to the earth, it would fall straight down towards the earth; so would everything in it, having the same acceleration as the spacecraft. It would feel just like being in orbit, till you encountered significant atmospheric resistance.

But if the spacecraft has some horizontal (tangential) component to its velocity, relative to the earth, it will travel some horizontal distance as it falls. If it has enough horizontal velocity, it will travel far enough to miss the earth. If it has just the right velocity, it will miss the earth but continue to fall around it at the same height. This is what it means to be in (a closed) orbit.

All things inside the spacecraft have the same acceleration due to gravity, so they fall with the spacecraft, at the same rate.

One thing in your list that I'd question: "You can lift a big man with one finger." Mass is just as real in freefall as it is when you're standing on the ground. You'd need something to brace yourself to lift this big man, but supposing you had that, it would still be much harder to move him than it would be to move a feather, and much harder to stop him after you've hurled him down the corridor!

5. Feb 24, 2010

### Misr

I don't think so
www.physicsclassroom.com/Class/circles/u6l4d.cfm

anyways this is enough

but gravity is not so small its just a little small than on the surface of Earth.

Oh yeah exactly its zero at infinity

Thanks so much

6. Feb 24, 2010

### Raekwon

Misr, are you trying to claim there is somewhere that has absolute zero gravity?

7. Feb 24, 2010

### Rasalhague

Yes.

If we consider the gravity exerted by more than one object, another place where the total gravitational field would be zero is the point between these objects where their individual gravitational fields are perfectly balanced, i.e. the vector sum of the fields is zero.

8. Feb 24, 2010

### Glen Bartusch

There will always be free radiations in interstellar space, whether the radiation be electromagnetic in nature or gravitational in nature. This is one of the two reasons why a temperature called "absolute zero" cannot be found anywhere in space (the other reason being due to a special class of particles called 'virtual particle pairs').

Remember, mass is simply defined as, "A resistance to a change in motion," and is a dimentionless quantity.

Lastly and most pertinently, gravity emitted (as gravitational waves) by any solid object must obey the inverse square law, meaning the effects of gravity diminish at the inverse of the square of the distance the measurement of the gravitational source is taking place. It's simply defined as "1/[the square root of] distance of gravitational measuring equipment".
Since things like the earth, moon, and even stars are not 100% dense (only black holes are), they will not obey the inverse square law exactly, but will come close. Take your gravitational reading of earth's mass, measure the diameter of the earth, then divide by 1/2. This will give you your reference point for the application of the inverse square (law).
And because of this inverse square law, the term "zero gravity conditions" can indeed be technically misleading. According to the inverse square law, gravity of the earth will taper off very substantially after several hundreds of nautical miles from Earth's surface and thus seem like true weightlessness, but there will always, of course, be gravitational waves--no matter how feeble--acting on any body anywhere in interstellar space.

An interesting fact: there is that region between earth and moon where gravitational waves ("gravity") from both bodies cancels each other out. This region is called the "Lagrange point". The anology would be the dropping of two stones near each other in a still pond: where their waterwaves meet would be analagous to the Lagrange point.

Last edited: Feb 24, 2010
9. Mar 11, 2010

### Misr

Some of your speech makes my question seem much more sophisticated than it really does

so I only want to know WHY :

1- we can lift a big man with one finger although gravity is reduced only by a little percent.
2- we jump up high and still hanging ALTHOUGH GRAVITY DOES EXIST.
3- Plant roots grow upwards

Thanks again .

10. Mar 11, 2010

### Raekwon

Only by a little? That would depend where you are, for example the moon has about 17% of the gravity that the Earth does. Because there is far less gravity, you will weigh far less.

Jumping high is because of reduced gravity.
"hanging" is just being in a state of freefall, everything falls together so it just seems like you "hang".

The roots of a plant will grow towards nutrients.

11. Mar 11, 2010

### BL4CKCR4Y0NS

If plant roots grow upwards in space, and you say that plants grow towards nutrients are you saying that there is more nutrients above the plant? I don't understand ...

12. Mar 12, 2010

### Raekwon

Gravity plays a part towards them always growing down on Earth, but people tend to think that it is gravity acting on the roots, this is not that case, you can get J rooted seedlings in cases of over or under supplies of water for example.

Either way, roots of a plant will always move towards a source of nutrition, gravity only changes where the nutrition is, some plants/trees will have deep roots to access the water stores there, sometimes they grow shallow to take advantage of any fresh rainfall, in some situations they may grow sideways, if there was say a rockbed below that it can't pass. I think there are a few NASA videos and details about plants in space, but I've not looked.

The stem itself will always grow towards a light source.

13. Mar 12, 2010

### BL4CKCR4Y0NS

14. Mar 12, 2010

### Raekwon

Gravity does act on roots yeah, but there's an Orchid in my house and the roots are growing up out of the pot, about 9 or 10 inches too, so it will depend on the type of plant.

15. Mar 27, 2010

### Misr

I mean when orbiting the earth.
for example , a man of 120 newtons will weigh only 88 newtons so still heavy not so light that we can lift him with one finger (i think so)
This is my question

Thanks very much

16. Mar 29, 2010

### Misr

Hello there??

17. Mar 29, 2010

### Max Faust

There is no "upwards" in space. (Really not on earth either, but because we are so small and the earth is so big it seems like that.) Modern hydroponic cultivation of various vegetables, for instance, have a "mist" system for feeding the plant which isn't relying on the root being located in any specific place and the foilage in another. However, that being said, many plants have "auxins" (a type of hormones) which are regulated by the tallest point (that reaches towards a source of light) and these will typically create the form we associate with them.

18. Mar 29, 2010