Help your kids visualize how mass creates a force called gravity and watch your own solar system come alive.

Mass-Gravity Series Part 1 of 3

This post and the next two were inspired by a video by a physicist using a large spandex sheet and showed how masses on that “space-time” fabric warp it and create the attractive force we know as gravity.  Since I’m a mechanical engineer, I have always loved physical analogies to explain abstract concepts.  How are you supposed to explain to a kid why there is gravity?  To be honest, I’m not a physicist so I don’t really know the real answer.  However, I CAN build this model and let my kids play and internalize the concept, understand orbits and effects of different masses.  Plus, it looks like a ton of fun… for all of us 😉

Here’s Dan Burns’ YouTube video which is a great demonstration and  inspired this project and the ones that follow.

So for this post, I’ll share how I put together this model with the materials I could get at the local big box stores and how it worked out for my kids and I.  I’ll get into some spin-off projects in my next 2 posts.

Bill of Materials:

  1. 3/4″ PVC tubing – cut into 4 pieces 4′ long each.  I bought 2x 10′ lengths of the flexible PEX  type which was easy to bend.  Available at home improvement stores – Lowe’s/Home Depot
  2. 4x straight couplings.  I got both the external and internal couplings to get a better connection
  3. 1 sheet of Spandex 5′ x 5′.  It was 20% spandex, 80% nylon.  You can get it online but I got it at Fabricland.  This was the pricey item – cost about $50
  4. 2 bags of 1″ binder clips (16 total) – got this from Staples
  5. A bag or two of marbles from Dollarama – they even come in different sizes and colours!  My kids loved them.

Assembly is pretty easy, check out my video below but basic steps are:

  1. Push external coupling on one end of each 4′ pipe.  Make sure it is all the way in by tapping it with a hammer on on the ground.  Add the internal coupling and tap it in firmly too.  You can always break it down into these 4′ lengths if you need to disassemble it for storage.
  2. Assemble the ring by putting the 4 tubes together
  3. Lay the ring on the spandex and use the binder clips to attach the fabric.  To keep the tension even I tried to do them one end and then the opposite end.  Ideally, going in order of the clock positions: 12:00, 6:00, 3:00, 9:00, 1:30, 7:30, 10:30, 4:30 and then filling in the gaps.
  4. Don’t bother trying to build a structure, probably more trouble than it’s worth.  Just find 4 chairs to use as supports.  Ideally, they should be at the same height so your sheet is level


So how did it work?  Well, it’s smaller than Dan’s model but it still worked out well and you can even do the the binary system (two large weights).  Even the earth-moon demo worked well which I thought was amazing.  But real question is how did the kids like it?  My 2 year old girl just wanted to grab it and flip it over but my 4.5 year old boy really enjoyed it.  He loved the marbles themselves but we discovered a few fun games while playing and that’s what it’s all about.  A few clips on our fun together below:


My mission through Daddy Engineer is to encourage people of all ages to enjoy engineering play.  Between work, kids and actually doing some of these projects, there’s little time left for blogging but I hope you enjoy my efforts.  Let me know what you think, your feedback and encouragement is much appreciated.

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