International Top Spinning Day, an annual event celebrating the simple pleasures of toys from the past is centered on Burlington, Wisc., today. The focal point will be the Spinning Top and Yo-Yo Museum. There, visitors can see more than 2,000 displays of tops, yo-yos, and gyroscopes. The tops range from modern to antique and come from around the world. There are tops that spin for hours, and even one that spins for days. Youngsters can learn about the physics that keep each of these delightful toys turning.  Tops and yo-yos are part of the $2.7 billion worth of toys manufactured in the U.S. each year.