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Today a friend's 6 year old sister asked me the question "why don't people on the other side of the earth fall off?". I tried to explain that the Earth is a huge sphere and there's a special force called "gravity" that tries to attract everything to the center of the Earth, but she doesn't seem to understand it. I also made some attempts using a globe, saying that "Up" and "Down" are all local perspective and people on the other side of the Earth feel they're on the top, but she still doesn't get it.

How can I explain the concept of "gravity" to a 6 year old in a simple and meaningful way?

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While great, this question is off topic for Physics.SE. It isn't about physics, it's about education and childhood cognition with a few physics metaphors sprinkled in. A large portion of any answer to this question could also answer "How do you explain <any complicated subject> to a 6 year old?" which makes this question about education. The rest of the answer is about simple gravity / falling / symmetry metaphors which makes this question too broad. –  Brandon Enright Jan 20 at 19:55
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Given this not about real answer, but about explaining to a child, should be moved to parenting.stackexchange.com . Lot of parents will find it useful –  Jayan Jan 21 at 8:30
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@BrandonEnright My thoughts exactly. If it's too advanced a topic conceptually for the child in question, then it likely falls under child development, education, or psychology. This isn't a physics question; it doesn't even fall under "pop" physics. Can we vote to close or migrate? –  JFA Jan 21 at 21:51
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@AmalMurali no, the point of this site is not to educate people, it's to allow people to ask high quality physics questions and get high quality answers. –  David Z Jan 25 at 9:50
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This question appears to be off-topic because it is about child psychology and education. –  David Z Feb 2 at 21:04
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closed as off-topic by David Z Feb 2 at 21:04

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15 Answers

up vote 90 down vote accepted

Having my own 6-year-old and having successfully explained this, here's my advice from experience:

  • Don't try to explain gravity as a mysterious force. It doesn't make sense to most adults (sad, but true! talk to non-physicists about it and you'll see), it won't make sense to a 6yo.

    The reason this won't work is that it requires inference from general principles to specific applications, plus it requires advanced abstract thinking to even grasp the concept of invisible forces. Those are not skills a 6-year-old has at their fingertips. Most things they're figuring out right now is piecemeal and they won't start fitting their experiences to best-fit conscious models of reality for a few years yet.

  • Do exploit 6-year-old's tendency to take descriptions of actions-that-happen at face value as simple piecemeal facts.

    Stuff pulls other stuff to itself. When you have a lot of stuff, it pulls other things a lot. The bigger things pull the smaller things to them.

    Them having previously understood the shape of the solar system and a loose grasp of the fact of orbits (not how they work—that's a different piece—just that planets and moons move in "circular" tracks around heavier things like the Sun and Earth) may be useful before embarking on these parts of the conversation. I'm not sure, but that was a thing my 6yo already had started to grasp at this point.

    These conversations were also mixed in with our conversations about how Earth formed from debris, and how the pull was involved in making that happen, and how it made the pull more and more. So, I can't really separate out that background; it may also help/be necessary.

  • Don't try to correct a 6-year-old's confusion about up and down being relative, but use it instead.

    There's a lot of Earth under us, and it pulls us down when we jump. If we jumped off the side, it would pull us back sideways. If we fell off the bottom, it would pull us back up.

    You can follow this up later with a Socratic dialogue about the relative nature of up and down, but don't muddy the waters with that immediately. That won't have any purchase until they accept the fact that Earth will pull you "back up" if you fall off.

  • Build it up over a series of conversations. They won't get it the first time, or the tenth, but pieces of it will stick.

  • Don't try to instill a grasp of the overall working model. If you can successfully give them some single, disconnected facts that they actually believe, putting them together will happen as they age and mature and get more exposure to this stuff.

All this is assuming a decently smart but not prodigious child, of course. (A 6-year-old prodigy can probably grasp a lay adult's model of gravity, but if that's who you're dealing with then you don't need to adjust your teaching.)

For some more context, this was also after my child's class started experimenting with magnets at school. I was inspired to attempt to explain gravity when my kid told me that trees didn't float off into space because the Earth was a giant magnet. (True! But not why trees don't float away.) Comparing gravity and magnetism might help, to give them an example of invisible pull that they can feel, but it might just confuse the subject a lot too since I had a lot of work (over multiple conversations) to convince my own that trees aren't sticking to the ground because of magnetism, even if the Earth is a giant magnet.

And, a final piece of advice that's incidental, but can help:

  • Once you've had a few of these conversations, play Kerbal Space Program while they watch. (Again, this comes from experience. My kid loves to watch KSP.) Seeing a practical example of gravity at work in it natural environment will go a long way to cementing the previous conversations. It may sound like a sign-off joke, but seeing a system moving and being manipulated makes a huge difference to a young child's comprehension, because it is no longer abstract or requires building mental abstractions to grasp, like showing them a globe does.
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<comments removed> Please do not hold long discussions in the comment, create a room in Physics Chat if you wish to discuss –  Manishearth Jan 24 at 9:30
    
And for everything else, "The Magic School bus Gains Weight" from scholastic is pretty good :) scholastic.com/teachers/lesson-plan/… –  Chris McKee Jan 24 at 16:15
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The misconception likely comes from a misunderstanding of "down". Making a 2-D drawing of the earth with buildings, people, and trees might help. For example, enter image description here

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This is even better corpsmoderne.itch.io/flappy-space-program –  rofrol Feb 14 at 22:37
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Wrap a ball (like a tennis ball) with a rubber band. Tell her to put her finger between the ball and the rubber band and try to move her finger away from the ball. Have her do this on all sides of the ball. Now explain to her how the rubber band is like gravity.

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This might make her think that gravity is a pushing force, pushing you down to the Earth, not a pulling force. While it might get the message across, it might also give her a very incorrect model of how the world works. –  Jeff Jan 20 at 16:27
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@Jeff There's no actual difference between pushing and pulling forces; they're the same vector. Gravity can be equally understood as pushing or pulling. For a great intuitive example of why the difference is meaningless: if you fall in a river, does it push you or pull you downstream? –  SevenSidedDie Jan 20 at 19:21
    
@SevenSidedDie you are right but in real life we don't use free vectors instead we have fixed vectors and hence it depends that where do you apply a force. –  Mukul Kumar Feb 9 at 13:39
    
@MukulKumar In "real life" vectors don't exist, they're just abstract constructs that are super-useful. We used fixed vectors (more often) because they're more convenient and result in simpler models, not because they represent any fundamental truth about reality (or pushing versus pulling). The map is not the territory. (A model that does care about pushing or pulling doesn't use a free body model. You have to get into engineering stressors and stuff before your model cares about push vs. pull.) –  SevenSidedDie Feb 9 at 23:34
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Rub a balloon with a cloth to induce a charge which will demonstrate "static cling", then attract small pieces of paper with the balloon. Once they see that static electricity attracts the small pieces of paper to the bottom of the balloon, then you can start explaining to them about 'the force'.

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This is my favorite answer because it gets to the heart of the matter with a demonstration of attractive force that uses a spherical object. The only thing that remains is to say that the gravity is basically the same idea, except you don't need to rub the object to charge it, you just need to be "heavy" (well, "massive", but that word is difficult). –  Mark Lakata Jan 20 at 20:21
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Pshhh. That's the law of magnetism, not the law of gravity. You'd have this kid flipping burgers! –  itcouldevenbeaboat Jan 21 at 14:49
    
@itcouldevenbeaboat Well, we thought that about the electric and weak forces too :D –  millimoose Jan 24 at 14:04
    
Didn't Mr. Wizard do this to help explain gravity? –  SpYk3HH Jan 25 at 4:18
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Here are some ideas:

a) Try to make her understand the concept of "force" : tie two balls on an elastic band. Make her pull them apart so that she gets a feel of force. Take an apple and drop it. Let her understand that if a force ( her hand) does not hold an object it is pulled by the earth, the way the elastic pulls the balls.

b) Then show her on a globe where you are. Show the vertical where the apple drops. You could then go to the force pulling towards the center, the way the elastic pulls along the line, and that it is the line that defines which way the force pulls, both for the elastic and the earth. Make the analogy that each point on the earth pulls along the line as if there is a band, towards the center.

good luck

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you can improve the example by tying two apples together - or by dropping a ball, but where's the fun in that ;) –  Christoph Jan 20 at 13:59
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Ask the child what "down" would mean to the people on the "other side" of the Earth.

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I was about to mention that you could ask the child "Where would the person fall to?" This will probably confuse her but it will get her to think. Sometimes answering a problem first involves helping someone understand the depth of what they are asking. If she thinks "they should fall up!" she should then realize that "this doesn't make sense" More questions will follow, but that's a good thing. Inquisition that leads to critical thinking will only help further her cognitive develop and that should be part of your goal in addressing her question(s). –  RLH Jan 20 at 17:27
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Take a magnet and hold it vertically, sprinkle iron fillings on either side of the pole. Iron fillings on the bottom side will be hanging. Then the child will get a feel that, it is possible for things to stay without falling down. You need not explain the concept of gravity for the child now. The child will create the explanation for itself (might also become next newton by creating a new concept).

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you could get really creative, and make a cylinder or sphere, using two magnets on the inside, and on the outside, on both top and bottom, objects representing people... –  aikeru Jan 20 at 16:32
    
@aikeru That was my thought, using a gerbil ball. I even imagined little, magnetized gerbil footies, but I quickly abandoned the idea :) –  Jolenealaska Jan 20 at 17:23
    
Now ask the child to remove the filings from the magnet. Wait five minutes. You have now successfully explained "raging berserker" –  Wim Ombelets Jan 23 at 8:23
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Just remember to coat the magnet with paper first. –  Dimensio1n0 Feb 6 at 13:57
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After carefully considering the OP's situation, I believe the focus falls on the rhetorical process. Following from this, my argumentative approach would be the following: stand firm about the fact that Earth is round, get the child to reconcile the inconsistencies.

The reason for this kind of approach is the child's behavior. The following quote is a script that I have repeated over and over in physics tutoring:

I also made some attempts using a globe, saying that "Up" and "Down" are all local perspective and people on the other side of the earth feel they're on the top, but she still doesn't get it.

Here, you presented an argument. But what followed after that argument? There's no apparent commentary on the argument by the child. I have no expectation that a kid would retort with consistent or event coherent counter-arguments, but the response seems to be missing altogether.

This is familiar to those of us with physics teaching experience. Wrong answers are always easy to deal with, and almost universally constructive. It's the lack of any model formation that blockades progress, and often leads them to switch majors to something non-technical because of the bad experience.

Consider the rhetoric to be like a chess game (with formally established rules for movement). As an educated adult, you probably don't have trouble responding to any move the child makes. If you do, ask another question here.

No rhetorical approach will be helpful 100% of the time. Counter-examples aren't always helpful either, but they appeal to a very particular example of inconsistent logic. If you ascribed to the bad logic before you see the counter-example, then it will accomplish it's purpose - demonstrating that you're wrong. I think the best response I've seen here was the following image (posted as a comment):

http://www.caloi.com.ar/caloidoscopio_new/byn/byn53.gif

This is physics perfection.

The absurd illustration makes the viewer abandon a view. You could reject that Earth is a sphere, or you could reject that gravity is always in the same direction. I suppose the option remains that people are presently, at this moment, falling off the side of the planet. I think that's what makes physics fun. For each model we build, there is a story that goes along with it. Most individual propositions can have a model built around it, changing everything else in the universe to accommodate. But once you are forced to explain multiple facts simultaneously, then you are in the process of building physics. Each model is a story. If you can start enjoying the process of telling those models/stories, then you are on your way to grad school.

I say physics involves two things: rationalism and evidence. Your model's consistency is dictated by reason, but which model applies is determined by evidence we get by the world around us (for which there is no mental shortcut). Here are some stories that do have consistency:

  1. Earth is flat, gravity is always down. The validity can more-or-less only be determined by measuring the Earth's shape.
  2. Earth is round, gravity is always the same direction. A privileged "top of the Earth" location exists, and everything else slopes down. You could verify this by observing a ball to roll off the edge of the world.

Maybe the best thing to do isn't to be correct, but show how you, yourself, enjoy being wrong. If they emulate that behavior, they will be fantastic scientists.

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There's a good chance you won't be able to make her understand how it works.

According to developmental psychologist Jean Piaget, children at her age tend to see themselves as the "center of the world", and are incapable of reasoning about it from any other viewpoint. The process is called egocentrism, and is the same reason why a kid gets confused when its mother calls its (the mother's) parents mother/father instead of grandmother/grandfather.

It won't hurt trying to explain, and she may gain some insight, but don't get frustrated if she doesn't.

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Almost all of Piaget's work has been called heavily into question; much has been refuted. Ironically, one reason is that it often fails to take into account how people in different parts of the world sometimes have different perspectives on things! Rather than trigger a discussion of developmental psychology, I will suggest this: The question here does not fundamentally depend on understanding anyone else's perspective. If only inanimate objects (e.g., cars and teddy bears) populated the other side of Earth, they'd still not fall off. –  Eliah Kagan Jan 20 at 18:42
    
These would make great questions on Cognitive Sciences :-) –  Josh Jan 20 at 19:14
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While this is good information about the cognitive issues involved, it doesn't actually answer the physics question at hand. –  David Z Jan 20 at 19:43
    
My 2.5 year-old gets that her grandma is my mum. –  a different ben Jan 23 at 8:05
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Why don't you try to explain that every object attracts other objects, but that in order for it to be felt, at least one of the objects must be very big? The earth is a very big object, so it attracts things towards it.

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Explain that since the earth is round, and people do not fall down (as there is no absolute "down"), they fall towards the center of the earth.

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He already said that: I tried to explain that the earth is a huge sphere and there's a special force called "gravity" that tries to attract everything to the center of the earth –  jinawee Jan 20 at 23:52
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Point out the fact that a ball falls straight down, and not sidewards. This is because it wants to go to the center of the Earth.

This is true everywhere. What we think is down is towards the center of the Earth, and this is true whereever we go.

(and then have a look at the globe and see what direction towards the center is)

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Tell him that down means "in towards the center of the Earth, no matter where you are."

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*her­­­­­­­­­­­ –  Awesome Apr 14 at 17:20
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What helped me to understand gravity is to model spacetime as a trampoline or a stretched bed sheet. Now put a melon on it, saying "This is earth which bends space." Now take a marble and say "This is you, also bending space, yet not as much". And no matter where you put the marble, it always goes "down" towards earth, as earth bends spacetime the most.

Yet what I think is important to convey that not only does stuff fall towards earth but that every mass has its own gravity field not entirely unlike a magnetic field.

You can go crazy with this experiment, saying the melon is the sun, a larger marble is the earth. Instead of letting the earth marble fall give it a sideway push and it will orbit the sun for a while.

You can even add a smaller marble as the moon and if you throw the earth and the moon marbles well enough, you will see the moon marble orbiting the earth marble while both orbit the melon sun.

There is a real nice example of this experiment on youtube.

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I don't think this is a good explanation. First of all it's 2D so there is no "up" and "down". The sheet analogy is not very good and difficult to understand to an adult (it should be stressed the importance of intrisic curvature). And Newtonian gravity should be also taught. –  jinawee Jan 22 at 9:41
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This will lead to the following SE question - "Explaining a 3D mapping of 4D space-time to a 6 year old" –  dav_i Jan 22 at 15:36
    
@dav_i, if you count time as 4th dimension, a comic book should do nicely. –  Cees Timmerman Jan 22 at 19:19
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This question is in fact a very challenging one and was first satisfactorily solved by Albert Einstein in the course of developing general theory of relativity from special relativity:

His first step toward a relativistic theory of gravitation was the proposition of the principle of equivalence. Equipped with this principle, he could explain some gravitational effects like gravitational frequency shift of light (or time dilation) and gravitational deflection of light:

enter image description here

but he couldn't account for the gravitational effects near gravitational sources like the Earth: he couldn't explain why the people on the opposite side of the Earth experience a gravitational pull in the opposite direction of the Earth. This effects are called Tidal effects:

enter image description here

He solved this problem by proposing a deep analogy between tidal forces and a property of surfaces called curvature. Basically, he proposed that space(time) can be represented by some curved geometrical objects called (pseudo-riemannian) manifolds. Thus, all you have to explain to him is this concept. I think the following picture, (although, with having the time dimension omitted, it's not precise at all) can help you/him a lot:

enter image description here

This pictures helps him to grasp the concept in a simple, geometrical and yet as scientifically precise as possible: all objects around the Earth fall toward the surface (center, of course) of the Earth. I think this explanation is in accordance with Einstein's quote everything should be as simple as possible, but not simpler.

To complete this answer, I explain (very) briefly the remaining steps to general relativity:

After this point, the only remaining step toward his theory was finding a relationship between this curvature and presence of gravity sources like matter and radiation. He arrived at his famous equation: $$\mathbf{G}=\frac{8\pi G}{c^4}\mathbf{T}$$.

in which the quantity $\mathbf{G}$ measures curvature of space(time) and the quantity $\mathbf{T}$ measures matter content.

Thus, a complete solution to the question why objects placed at different locations around the Earth experience forces in different directions (all toward the center of the Earth) necessarily needs a general-relativistic argument.

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I would downvote this if I could. How is this answer appropriate for a 6 year-old? –  Disco 3 Jan 22 at 12:09
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Preschool Kids Spontaneously Employ the Scientific Method, but this answer still lacks some steps in my case as i've been a preschool kid and still don't get this. –  Cees Timmerman Jan 22 at 19:15
    
I added more explanations to the crucial part of the answer. (5th paragraph) –  user215721 Jan 22 at 20:29
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So... why don't people slide to the bottom of the Earth? What do tidal effects have to do with it? I'm afraid your answer doesn't actually answer the question. –  iamnotmaynard Jan 22 at 20:46
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An easier way to illustrate the principle would be to set a small ball or marble on a sofa cushion. Then you or the child sit on the sofa a few inches away. See how the ball rolls toward you? Now explain that the difference in size between the earth and a person is much greater than the difference between you and the ball. Then explain that there's a force called gravity that causes very large objects to pull small objects towards them. –  djheru Jan 23 at 18:08
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