Chalk Top

Principle: Learn about angular momentum and how it can keep a top upright. Also see how tops precess around an axis. (http://hyperphysics.phy-astr.gsu.edu/hbase/top.html)

Interaction: Turning the handle on top will spin-up a metal flywheel inside the top. When placed on the ground, the top will then slowly start spinning. Children can load different colors of chalk into the top, wind it up, set it on the ground, and watch the top create patterns on the pavement. 

Construction: The outside body of the top as well as the hand crank would be made of a durable, injection molded plastic. The bottom tip may be composite reinforced to resist wear from the ground. The internal gears and flywheel would be made from waterjet-cut stainless steel. The holes for the chalk would have an easily adjustable collet to accommodate different chalk sizes. 

Cost: This is the most expensive of my three concepts as it is larger (~8" diameter) and has many components (some of which are steel). I would estimate a sale price of ~$30. 

Durability: The tip is designed to be extra-durable to account for the abrasive cement and concrete surfaces the top is intended to be used on. The plastic construction can handle small drops, but high falls onto pavement may break the outer shell. 

Safety: While relatively large for a top, even at speed the top will have relatively little energy and would not hurt anyone who stops it with their hands. However, since it takes some effort to wind it up, and kids may try to eat the chalk, this product is recommended for ages 5+ . 

Learned: Many people were concerned with the resistance of the chalk on the ground when this idea was presented. A spray chalk system may be needed instead, but I'm not convinced normal chalk would not work. I also realized how scale is not intuitive in drawings, as I had a good idea of the size and weight of the top in my head, but others did not.