Gravity well with rock in the center

Gravity Wells

I haven’t blogged for a while because I’ve been busy with work, family and other writing projects. I’m trying to write a 5,000 word short story for a contest. (It is hard for me to write “short,” even though I have 4,000 more words to work with than for the last short story I wrote for a contest.)

But now that my school year has started and I am settling into a routine, I want to get back to more regular blogging again. I also want to include more science posts in this blog, so with today’s post I want to combine two concepts and make a Mundane Monday post about gravity. In fact, what could be more mundane than gravity? All of us earth-dwellers experience it every day. We can’t get away from it–literally!


In my teaching work, I am an Instructor with an educational non-profit called Science from Scientists. We visit public school classrooms and work with the classroom teachers to provide hands-on science lessons for students in grades 4-8.

For this week’s Mundane Monday photo challenge I show the apparatus that I used to teach about gravity to my 8th grade students last week. It consists of a raised hoop made of PVC pipe, with a cloth stretched over it and clamped. I had to get there early with my co-teacher to set four of these wells up in the middle of the classroom.

Gravity wells in the classroom
Not a kettle drum!

The green fabric represents the “fabric of spacetime,” and the idea is that if you put a massive object in the center, such as a rock, you can model what happens when one massive object attracts another at a distance due to gravitational force.

Gravity well with rock in the center
A rock bends the fabric of space-time to attract marbles

And an even more massive object will bend the fabric of space-time even more:


These mundane experiments remind me of the uses and limitations of model building. Many of us may have seen the spiral coin collectors that operate on the same principle:

These are fun to watch (and they may encourage people to donate more coins than they would into a plain box). But the coins, and the marbles in our curriculum kits, all end up in one place: the center, or the bottom of the well. Real stars, planets, and moons keep orbiting because they are going fast enough never to fall to the center, and they are not subject to friction in space.

I hadn’t realized until I was watching the movie Hidden Figures over the weekend, that it wasn’t so long ago that we humans didn’t understand how all this works. There is a scene in the movie in which NASA scientists are discussing how to move the satellite from a stable orbit to landing back on earth. They need to define a go/no-go point in which the satellite’s orbit will change from an ellipse into a parabola, so that the satellite will splash down near the Bahamas where the astronaut and capsule can be recovered by a rescue ship. Back then all of the calculations necessary for planning these trajectories were done by hand, by a group of human “computers.” The best human computer was a woman named Katherine Johnson, who did the calculations in her head or on the blackboard, quickly and error-free. Nowadays when I have more computing power here on my lap than they did in all of NASA in 1962, it’s easy to forget what an achievement it was to bring John Glenn safely home.

Gravity Waves
Gravity Waves. Image credit: NASA


For the Mundane Monday Challenge #128.


13 thoughts on “Gravity Wells”

    1. My understanding is that white dwarves are husks of old medium-sized stars. I think you are talking about black holes, when you mention “too much gravity.” Larger stars (>8X the size of our sun) won’t turn into white dwarves. They will explode into supernovae and leave behind a neutron star or a black hole. A black hole has so much gravity condensed into a small space that even light cannot escape.

      Liked by 1 person

  1. Hi KL – what an interesting post … and I bought the book Hidden Figures – as I’d missed the film when it was shown here … I do enjoy learning – more about our world … I don’t understand the maths! Cheers Hilary

    Liked by 1 person

    1. I don’t think you have to understand the math to enjoy the film. (The actress who played Katherine said she didn’t even understand it!) I just saw it on DVD this past weekend. I’ve heard a couple people say that the film is better than the book. I’ve got so much other reading on my plate that I don’t think I have time for the book!


  2. Who says you can’t teach an old dog new tricks? Thanks for educating some of us while showing how you tech the younger generation how science is real and not just text books. I would have enjoyed you as my teacher many moons ago. Good blog and I’m thinking that you should not problem with your 5k short story – just layout your story idea like your science project lesson then put words to it. 😊

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  3. There was a time when I was in a Masters of Education program, and found myself sitting in a 8th grade social studies class waiting for it begin at the edge of the classroom. A few of the students sat in the chairs next to me and of course starting asking me questions about why I was there (to shadow the teacher), what i was going to teach. At that time, I was working on my endorsement in science and one of them leaned in, and said with the upmost sincereity:

    “Please make it interesting.”

    The other too agreed with enthusiasm.

    Looks like you know how to do that.

    [For the record: I ended up dropping out the Master’s program just before my student teaching was to begin, and transferred to the creative writing department, because I didn’t have the skill sets and emotional groundedness to teach. I have the upmost respect for those who are able to engage and teach our youth, especially in ways that don’t bore them and turn them off to learning and creativity, whether in the sciences or the arts.]

    Liked by 1 person

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