|Why and how is there no gravity in space?|
|Question Date: 2020-04-23|
Hi Evita, very good question. It may seem there is no gravity in space, but gravity is everywhere. Gravity decreases the further away you go from something. So in space, you're far away from planet Earth and you feel less gravity. Let's use our imaginations for a second. So you're a brave astronaut orbiting the Earth. Leaving your ship you feel weightless! In fact you and your ship are constantly falling towards the Earth from gravity. Nothing stops your fall, so you feel weightless. Riding a roller coaster or a fast moving elevator feels somewhat similar!
When we are on earth and we jump up, gravity pulls us back down. But in space, astronauts do not fall to earth. Therefore it might seem as if there is no gravity in space. It turns out this is not quite what is happening. Gravity exists because all objects with mass exert a pull on other objects. The greater an object's mass, the harder it can pull other objects toward it. In this sense gravity can exist everywhere, with the most noticeable gravity in our experience being that of the earth, the most massive object near to us. The distance between two objects also turns out to be important in determining the gravitational force that one object exerts on another, with the magnitude of the force of gravity of object 1 acting on object 2 decreasing with the square of the distance between objects 1 and 2. That is G ~ 1/r2.
In space, astronauts in orbit are far from the earth and thus experience a reduced gravitational force. This is part of the reason they appear to experience less gravity and do not fall to earth. There is a second, very important part: the astronauts in orbit are actually constantly falling toward the earth. They are constantly subject to earth's gravity, but they are also constantly traveling at their orbital velocity, which is perpendicular to the force of gravity. The astronauts are continuously accelerated by the force of gravity, and their velocity continually changes not in magnitude, but in direction, resulting in the circular path of their orbit around earth. The consequence of this is that they are actually in free fall, along with the space station and the other astronauts around them.
The earth's gravitational force imparts a constant acceleration to all objects regardless of their mass--you may have observed this by dropping a heavy object (such as a bowling ball) and a lighter object (such as a tennis ball) from the same height and watching them hit the ground at the same time. Therefore the astronauts and the space station are being accelerated at the same rate, and relative to one another, they do not change speed. Because of this, even though they are in free fall relative to the earth, they can appear still relative to one another, and this gives the illusion that neither is acted upon by gravity (in the sense that gravity makes you fall). This got a little complicated, so if you need clarification, please feel free to reach out to scienceline again with any questions, and I or another scienceline scientist will be here to help.
Thank you so much,
There actually is gravity in space!
The equation for gravity is
G m1 m2/r2.
G is a constant that we don’t need to worry about for now. m1 and m2 are the masses of object 1 and 2, and r is the distance between the objects. What this means is that anything that has mass will both exert and experience a force of gravity, and this force weakens as the objects get father away from each other.
When you are in space, you are farther form the earth, so its gravitational force is weaker. While weaker, the force of gravity is still very much so present because of how large the earth is. However, when you are closer to another large object, say an astronaut on the moon, the moon’s gravitational pull is the dominate force, which is why the astronauts stay on the moon’s surface, rather than being pulled back to earth.
But we have all seen videos of astronauts seemingly floating in space, which certainly makes it seem like there is no gravity. When in orbit, space shuttle and astronauts are actually experiencing earth’s gravity, they are just in a free fall around the earth, rather than a fall directly towards the surface of the earth. They are being pulled towards the earth, but continually “miss it” resulting in an orbit rather than a crash landing. While they are moving very fast in orbit (i.e. have a high velocity), they have little to no acceleration (meaning the velocity is relative constant).
Acceleration determines force, so this means they do not experience any appreciable net force, so relative to the objects around them, they appear to float.
This question relies on an incorrect assertion - there IS gravity in space. Gravity is the force that attracts all bodies with mass towards each other.
The magnitude of gravitational force between two objects is given by the formula
F = G*M1*M2/r2 (where G is the universal gravitational constant, M1 and M2 are the masses of the two objects, and r is the distance between the objects). As can be seen, this force never disappears, so it must also permeate (extend through) space.
This is extremely important because gravity is the force that holds the universe together, including keeping Earth in orbit around the sun.
This may be confusing given that in videos taken in space, such on the International Space Station, astronauts appear to be weightless, i.e., appear to not be pulled down by gravity. In reality, they are still affected by gravity and are constantly being pulled toward Earth. BUT, they are also moving sideways fast enough that they always miss the surface. The reason the astronauts do not press against the floor of the spaceship is that the ship is falling at the same velocity as the astronauts. More explanation of this phenomenon can be found at these ScienceLine questions.
There is gravity in space.
Something that is falling will not generally notice that gravity is acting because everything it is in contact with will be falling at the same rate. Being in orbit around the Earth or anything else is basically falling, but instead of hitting the ground, you have so much sideways speed that you miss the planet that you're falling towards, and instead wind up orbiting it. The International Space Station has about 90% the gravity that you do on the ground, but it's moving sideways so fast that it doesn't fall down.
There's a little bit of gravity in space [microgravity]. Gravity gets weaker and weaker when objects get farther apart, and objects in space are far apart.
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