Riding a Ripstik involves angular momentum. You start out with zero momentum because you're not actually spinning. When you twist your upper body one way, your legs and the board rotate in the opposite direction to keep the angular momentum equal to zero. I'm not sure if you can really see it in the picture, but my brother's body is rotating to the left, so his lower body and the Ripstik rotate (sort of) to the right. Momentum is conserved because there is no external torque acting on you.

Ok, so I tried the spoon/fork/toothpick balancing thing and it actually worked :) It kind of reminded me of the balancing bird that we used for one of the labs. The handle of the fork and spoon are kind of like the bird's weighted wings that are extended below its head. That's why I think the CM is located in the air, between the ends of the fork and spoon (which I guess is the support area). This "experiment" proves that the CM is not always at the geometric center but depends on the distribution of the object's mass. It was also like the lab we recently did where we had to balance a 200 g mass at the 5 cm mark of a meter stick. The torque of toothpick's weight had to equal the torque of the spoon/fork (I think).

I was playing Mariokart DoubleDash this weekend, and I realized that it has a lot to do with centripetal force. It may not be real centripetal force since it is just a videogame, but anyways...Centripetal force is important when making turns. I noticed that I had to apply the brakes a lot to make it around some bends (see the sparks in the picture?). In this case, friction was the centripetal force. My cart would spin out when there wasn't enough friction. The centripetal force was also always directed inward. Mariokart DoubleDash even involves bouncy collisions because you get to throw shells and firebombs at other players. The mushrooms also make you accelerate :)