Chop Top

Make a top that creates colors from black!

This is one of the 48 projects for our Instructables: Made In Your Mind (IMIYM) exhibition at the Children’s Museum of Houston showing from May 26, 2012 - November 4, 2012. Produced in partnership with Instructables, IMIYM is an exhibit where families work together to build different fun, toy-like projects that help construct knowledge and skills related to science, technology, engineering, and mathematics while instilling a “do-it-yourself” attitude in kids so they feel empowered to explore, tinker, and try to make things themselves. To learn more, check out the article here.

This project was originally conceived of by Children's Museum of Houston staff. After some searching, we didn't find anything on Instructables like it, but there may be some on Instructables that are similar, in which case please let us know through comments. Often, the materials and process for building our projects are designed for use with a large number of visitors (we see over 800,000 annually) and the need to ensure safety in a mostly non-facilitated environment. So, yes, many of these projects have room for improvement in both materials and methodology, which is PRECISELY what we want to encourage the kids to do. So please do share your ideas for improvement and modifications!

Step 1: What You Need:

We are selective in our materials for cost, ease of use, and safety due to our high traffic (800,000 visitors annually). So, for our purposes, this design worked best. But you may have other ideas - please share!

1 - 8½” x 11” Chipboard (we buy ours in bulk from U-Line, but a cereal box will do the trick)
1 – Chopstick (we purchase ours in bulk from Asian Food Grocer, but you can get a pair from your local Chinese take-out place.
1 – Chop Top Template (see attached file - it is a version of a Benham's Disk - you can Google up several versions)
4” Round Stencil (we used a piece of PVC drain from our Shop's scrap area, but a compass that can draw a 4" circle would work just as well)
Scissors
Tape
Pencil

Step 2: The Video

We offer optional video segments of each step for this project in the actual exhibit. Here is a compilation of all the steps.

Step 3: Step 1

Use a 4” diameter stencil or a compass set to a 2" radius to trace four circles onto the chipboard. Make sure to also mark the center of each. Cut out each circle

Step 4: Step 2

Fold each circle in half with the center mark on the outside. Cut a small hole in each circle (ideally smaller than the diameter of the chopstick) at the center mark and unfold them. Not the end of the world if they are bigger than the chopstick.

Step 5: Step 3

Tape all four circles together along the outside edge. Keep the amount of tape balanced.

Step 6: Step 4

Cut out the Chop Top Template (see the PDF with the materials list). This is just a Benham's Disk - if you google it, you can find lots more examples. You could even try to draw your own (and if you do, please share pictures and your experience!). Use the chopstick or pencil to carefully punch a hole in the center of the template

Step 7: Step 5

Using loops of tape under the template, stick it to the cardboard disk. Do NOT put any tape on top of the template.

Step 8: Step 6

Slide the template and the four circle disk onto the chopstick through the center holes. Tape the underside of the disk to the chopstick about 1½ - 2 inches from the tip. Do not put tape on the paper template. Try to make the disk as perpendicular as possible to the chopstick.

Step 9: To Use

To spin it, hold the chopstick between your hands, then slide one hand over the other. Watch the Benham's Disk as it spins – you should see colors!

The physics for why tops don't fall down when spinning is acutally spectacularly complicated. So apologies to physics aficionados for this simplification: when you spin a top like the Chop Top, you provide a force in a circular direction. The spinning top’s inertia keeps it moving in a circle, so gravity is unable to pull it down. Eventually, friction slows down the top enough that gravity is able to overcome the inertia and pull it down.

As for the colors, this is a type of optical illusion known as a Benham’s Disk where certain patterns of spinning black and white cause people to see colors. But the reason why is still unknown after over 100 years!

Comments

[Xixfas]

" Asian Food Grocer"
:)

[CMHouston]

So, to get a little more into the physics of top spinning, it comes down to angular momentum. From what I understand, and my higher level physics is a bit rusty (and my calculus even more so :-), so please correct me if I'm wrong anywhere.

As the disk spin it has inertia (Newton's First Law of Motion). Think of one single point on the disk - that point tends to keep moving in a straight line. However, the solid disk forces it off of that straight line, resulting in an acceleration (a key point: in physics terms, acceleration is a change in speed and/or direction). Where there is acceleration, there is force, namely angular momentum which is what opposes the force of gravity. As long as angular momentum is greater than force of gravity, the top will spin.

The amount of this force opposing the gravity is based on the speed of the disk and the mass of the disk. So, as friction slows down the top, the angular momentum decreases until gravity is the greater force causign the top to tip over. Also, an off-center/off-balance top with have uneven angular momentum and that will cause it to fall over.

[wilgubeast]

That's so cool! Also, you should enter this into the Make it Real Challenge along with the Education Contest. Since you used a computer to make the template, this absolutely qualifies.

Also, I know there are at least a handful of physics aficionados on Instructables who could explain what forces are acting upon the top. Possibly in the comments, guys?

[CMHouston]

Thanks for the suggestion. I'll do that!