Today’s Wonder of the Day was inspired by Ms. Sanna's 2nd Grade Class from Batavia, IL. Ms. Sanna's 2nd Grade Class Wonders, “How does a toy top spin without falling down?” Thanks for WONDERing with us, Ms. Sanna's 2nd Grade Class!
When you think of your favorite childhood toys, what comes to mind? For some children, older video game consoles may hold good memories. Others might think of action figures from an animated movie or a doll.
If you ask the same question of older adults, such as grandparents, you'll probably hear about a variety of simpler types of toys. They probably have fond memories of slingshots, rubber balls, and battles between groups of tiny green Army men.
There's another old toy that most children play with at some point in their lives. It comes in a wide variety of shapes and colors, but its function remains the same across varieties. With a flick of your fingers grasping a small post on the top, you send the small object spinning wildly across a tabletop or the floor.
What are we talking about? The spinning top, of course! Whether you spin the top with your fingers or hold the top upright while you pull a string to start it spinning, the top spins rapidly, miraculously staying upright for a long time before eventually beginning to wobble and finally fall back onto its side.
When it comes to old toys, the spinning top is really, really old. No one knows exactly how old it is, but it's definitely been around for thousands upon thousands of years. It's possible that the first spinning top toy was nothing more than an acorn put into motion by a curious kid.
If you've ever played with a spinning top, you can see how fun it would be to spin an acorn in a similar way. Over time, it was probably a natural progression to begin carving pieces of wood into acorn-shaped toys.
Compared to modern toys, the spinning top may seem quite simple. The scientific forces that make it such a fun toy, however, give us a brief peek into advanced physics. Indeed, if you asked a physicist how a spinning top works, you'd receive a fascinating — and lengthy — explanation.
Without getting into advanced physics and mathematics, let's take a look at some of the basic forces that make a top spin. When you spin a top into motion, you're applying a force that converts the top's potential (stored) energy into kinetic energy, or energy of motion.
As it spins in its upright position, it rotates around an invisible vertical axis. The principle of conservation of angular momentum holds that the top would keep spinning indefinitely if there were no other external forces acting upon it.
However, that is not the case. Tops are never perfectly balanced and weighted. Moreover, the surfaces they spin on aren't perfectly level either. These imperfections allow other forces, including friction and gravity, to come into play.
When it's spinning, a top balances on a tiny tip. This minimizes the amount of friction generated by its contact with the surface below it. Eventually, though, friction will begin to slow the top's spin. When this occurs, the top begins to wobble, demonstrating a scientific principle called precession.
As it begins to wobble, the axis of the top tilts to the side, which allows the force of gravity to exert a force known as torque on the top. The effect of the torque is to create additional spin while also causing the top to precess (swing) outward. As the top's spin continues to slow, it precesses faster in an attempt to conserve its total angular momentum. This is why the wobbling gets worse right before it falls and comes to a stop.