Main content
Course: Middle school Earth and space science - NGSS > Unit 1
Lesson 2: Galaxies and gravityGalaxies and gravity
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.
Want to join the conversation?
- What would happen to us if the Andromeda galaxy colided with the Milky Way?(13 votes)
- 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?(36 votes)
- So is your weight just the weight of gravity pulling you down?(5 votes)
- Close, your weight is the force of gravity pulling you down (and if you're talking about how much weight you have, that's called your mass) like when you jump up in the air, falling is the force of gravity pulling you down back to earth, you know (not to be a downer or something) you can't stay up in the air for ever, upvote if you got the joke😄
If that still doesn't make sense, there is a physics video that goes more in depth about it, it's unit 1 lesson 4, AP college physics.
I hope that helps!(19 votes)
- 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?(4 votes)
- 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?(15 votes)
- if our body touched space without a suit what would happen(5 votes)
- 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.(6 votes)
- 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)
- I have heard this one before. If you did this, than you would take 40 minutes to get to the other side, than you would fall in and take 40 more minutes to get back, and so on.
Does that help?(2 votes)
- How do we know the Earth is a planet(3 votes)
- 1.Earth moves around the sun
2.It's big enough to have enough gravity to make its shape spherical
3.It has a clear path while revolving around the sun.(5 votes)
- What would happen if gravity never existed?(2 votes)
- Then the Earth wouldn't have formed, the Sun wouldn't have formed, the Solar System wouldn't have formed and so on and so forth. either the universe would just be some dust and gas floating around or the big bang wouldn't have happened.(2 votes)
- why does space rotate(4 votes)
- It dosen't, space does not rotate in fact, Space is a three-dimensional continuum containing positions and directions. In old physic, physical space is often conceived in about three dimensions. Modern studies usually consider it, after a long time, to be part of a limitless four-dimensional continuum thought of as spacetime. It is the void in which there is nothing but atoms. As the universe grows, space separates all of the universe farther and farther away from us.(2 votes)
- If Voyager only traveled 0.1% of the distance to the closest star, then how do we know that Andromeda is gonna smash into us? SO CONFUSING!(4 votes)
- The Andromeda Galaxy is approaching the Milky Way Galaxy at a speed of about 300 kilometers per second (186,000 miles per hour). This collision is inevitable and will occur in about 4.5 billion years. The galaxies will pass through each other, but their stars will not collide directly. Instead, they will be thrown into different orbits around the new galactic center. The collision will result in a new, larger galaxy, often referred to as Milkomeda, which will be an elliptical galaxy. The supermassive black holes at the centers of both galaxies will eventually merge, emitting gravitational waves as they do so. The solar system will likely be tossed farther from the galactic core than it is today, and there is a small chance it could be ejected from the galaxy entirely.(1 vote)
- why to earth have to be part of a galaxy and does the earth have to be in the center og the galaxy.(3 votes)
- The Earth is not the center of the galaxy.(3 votes)
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.