Tag Archive for Hula Hoop Physics

How Hula Hoops Work

Physics by Philo Hagen

While we all spend a lot of time inside our hoops spinning things up, have you ever given any thought to what is actually taking place scientifically? How do hula hoops actually work?

While we can hoop it up on various parts of our body, for this discussion let’s focus on traditional waist hooping. Hula hooping involves the steady, parallel oscillation (or periodic motion to and fro) of an unstable ring around a person’s waist. When you stand in the middle of your hoop, you become the axis point, the center of the ring’s rotation, and as the axis point, you then become the source of the hoop’s movement. You are the fuel in the hooping equation. When you move your body to propel your hoop around you, you are actually exerting a turning force known as torque, which is basically a twisting force that tends to cause rotation. Torque is necessary to maintain the centripetal force which keeps the hoop spinning around the axis, and yes we are talking about centripetal force, not centrifugal force which is a common misconception. Centripetal force is a force that makes a body, such as a hoop, follow a curved path. It is always directed orthogonal to the velocity of the body, toward the instantaneous center of curvature of the path. The amount of force that is needed depends upon a couple of things, one being the size and weight of the hoop itself and how it relates to the size of your waist. An adult-size or larger or heavier hoop will move more slowly requiring less torque, while a smaller or lighter hoop will require more.