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Galaxies and gravity

NGSS.MS:
MS‑ESS1‑2
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MS‑ESS1.A.2
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MS‑ESS1.B.1
Earth is part of the solar system, which is part of a galaxy, which is part of a galaxy group. All of these systems are held together by gravity, a force that pulls objects with mass toward each other. Created by Khan Academy.

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  • aqualine ultimate style avatar for user SD360
    What would happen to us if the Andromeda galaxy colided with the Milky Way?
    (7 votes)
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    • female robot amelia style avatar for user Johanna
      Because there is so much space between the stars in galaxies, it’s not very likely that any one star (or our solar system) would be significantly messed up from this happening. The galaxies would effectively pass through each other (imagine ghosts going through each other) while deforming a bit. Then the galaxies would gravitationally attract each other again and keep going back and forth a few times until they merged to form a new, bigger galaxy. You can actually look up pictures of spiral galaxies in various stages of merging to get an idea of what this might look like.

      The Milky Way and Andromeda Galaxies aren’t projected to collide for another five billion years, though, which is also when the sun is going to “die” after running out of hydrogen.

      Does that help?
      (3 votes)
  • primosaur ultimate style avatar for user 🅲🅷🅴🆆🅸🅴🅰🅻🅻
    So then, if you were to make a hole from one side of the earth to the other what would happen? Would you have to crawl out? Would you fall out on the other side? Or would you remain in the same spot?
    (6 votes)
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  • male robot johnny style avatar for user rob27bra
    if our body touched space without a suit what would happen
    (4 votes)
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    • aqualine ultimate style avatar for user Mark
      The problems that your body would face are all connected to space having no atmosphere. That means (1) no oxygen to breathe, (2) no confining pressure so the gasses in your body would expand and make you swell, and (3) no protection from the Sun's rays so you'd quickly get a sunburn. After a few minutes you'd be dead.
      (3 votes)
  • blobby green style avatar for user Jasmine Lin
    What are some other examples, except for the Andromeda Galaxy, of galaxies in our local group? Also, have scientists discovered and named galaxies out of our local group?
    Another question: at , the narrator says that it’s a lot harder to throw you into the air than a ball. Doesn’t that also depend on how much you weigh? Or is it like the more you weigh, the stronger the pull of gravity is on you, and THAT’s why to other people, you weigh more?
    (3 votes)
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    • mr pants purple style avatar for user The Purple Bear
      I'm not sure the extent of "local group" is, but here are some interesting galaxy examples. The Saggitarius Dwarf Elliptical Galaxy, The Antennae Galaxies, and M82. Fun fact, we are set to collide with the Andromeda Galaxy in the future (not in our lifetime). Weight is just the force acting on an object due to gravity. The formula for force is F=m*a, F is force (weight), m is mass, a is acceleration (gravity). The "pull" of gravity is constant for everything in Earth's domain, so the weight depends on the mass of an object. If you are 10 kilograms more than a ball, you will weigh more than a ball, which will make you harder to throw. So, you are kind of right, the more something weighs, the harder it is for you to throw it, but you cannot have a stronger pull of gravity on you as compared to something else, because gravity is constant.
      (4 votes)
  • duskpin ultimate style avatar for user nalan.kanish
    If I have more mass than a tiny ball, will I attract the ball in space (when it is quite near me), where there is no other force?
    (3 votes)
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    • female robot amelia style avatar for user Johanna
      Everything with mass gravitationally attracts everything else with mass. Even if the objects’ masses are small and they’re very far apart, gravity will still have some force.

      This means that even right where you are, you and the little ball attract each other. It’s just not very noticeable because your masses are very small, and your attraction with the earth is much stronger.

      Also, it doesn’t matter so much who has more mass. The force of gravity the ball exerts on you is equal to the force of gravity you exert on the ball. Think about it: if we’re not measuring your speeds from any “fixed” reference point, is the ball approaching you, or is it the other way around?

      Far out in space, you and the ball would attract each other with the same small force, but that attraction might be the strongest one acting on you. Left undisturbed, you and the ball would approach each other very, very slowly.

      Does that help?
      (4 votes)
  • blobby green style avatar for user edmonlul000
    Why isn't their gravity in space?
    (2 votes)
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  • aqualine ultimate style avatar for user apexwannabelegends35
    so when they collided will there be people alive like maybe a few years before and say will there be life after the effect if so how will it effect us in theory which sounds scary
    (2 votes)
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  • mr pants teal style avatar for user benjamin.santacruz
    i dont anderstend by a lot\
    (2 votes)
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  • blobby green style avatar for user Leilani
    Is it that small I think it’s more stars in the Mickey way
    (2 votes)
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  • blobby green style avatar for user Trish
    our sun is a star !!? how why is the sun a star ? how whas it formed ??!😐😐😐🎇🎇💁💁
    (2 votes)
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Video transcript

- [Instructor] Hello, everyone. Today, we're going to be talking about galaxies and gravity. We know the Earth is a planet that is in orbit around the sun. This is called the heliocentric model. And the solar system is an enormous space for us, encompassing every place that humans or our robots have ever been. But it's actually quite small, cosmically speaking. Even our furthest spacecraft, Voyager 1, has only traveled less than 0.1% of the distance to the nearest star. Our solar system is just a small component of a much, much larger set of structures. The sun is just one star of hundreds of billions of stars in our galaxy, which is called the Milky Way. And our galaxy is one of several dozen in our galaxy group, which is called the Local Group. Other galaxies might belong to larger collections that are called galaxy clusters. Now the same thing that holds Earth in its orbit around the sun is what holds together massive groups and clusters of galaxies: gravity. This is the same as the gravity that makes a ball fall back to the ground when you toss it up into the air. Gravity is a force that operates between two objects that have mass and tries to pull them closer together, whether those objects are a ball and the Earth or two galaxies. Now the strength of this pull depends on two things. First is the mass of both objects. So as either object gets more massive, the strength of gravity increases. For example, you have a lot more mass than a ball. So the force of gravity between you and the Earth is pulling harder than the force of gravity between a ball and the Earth, and that's why it's a lot harder to throw you into the air than a ball. Gravity also depends on the distance between the centers of the objects. As the objects get farther apart, the strength of gravity decreases. For example, if there is a ball on top of Mount Everest, the pull of Earth's gravity on it is actually slightly less than the pull of gravity on that same ball at sea level, because the top of the mountain is farther away from the center of the Earth. Now, this is a very small effect, less than a percent difference, because the difference between sea level and mountaintop is still very small compared to the distance to the center of the Earth. But that's just on Earth. We know that things in space are really far apart. The Earth is almost 93 million miles, that's 150 million kilometers, from the sun. So if gravity is weaker when objects are farther apart, then in order for gravity to be keeping these structures bound together, they must be really massive, and they are. The sun has a mass of about two nonillion kilograms. That's 10 to the power of 30. And the Milky Way galaxy, which is about a quintillion kilometers in diameter, has a mass of about 1.5 trillion times that of the sun. So thanks to their high masses, objects like our Milky Way galaxy and our nearest neighbor, the Andromeda galaxy, which are the two largest galaxies in the local group, can be pulled together by gravity, even across millions of light years. In fact, gravity between our two galaxies is so strong that it's actually pulling the Milky Way and Andromeda galaxies together into an eventual collision. But eventually in this case means almost 5 billion years from now, so no need to worry. To review, in this video we covered how the Earth is part of the solar system and our solar system is part of a galaxy, and our galaxy is part of a group. Galaxy groups, galaxies and solar systems are all bound together by the same force, that of gravity. Gravity is a force which tries to pull objects with mass closer together and it is weaker for less massive objects or for objects that are farther apart. Thanks for watching and I hope you learned a little bit of something.