Tag Archive for Centripetal Force

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 the 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.

Inertia then really helps us out too by enabling the hoop to continue its angular momentum after our initial application of force, but as we all know that won’t happen for long. As the hoop moves against your body and through the air, friction inevitably slows it down and this will cause it to fall. If you don’t want gravity to win the war, however, then you have to expend more effort to keep your hoop going using regular pulses, staying just a little ahead of your spinning circle in order to aid in the ongoing momentum.

While we don’t really need to understand the physics to actually do it, given that hooping comes naturally to so many of us if you simply have the right size hoop, from a biomechanical standpoint hooping is a rather complex task. Scientists are still working out exactly how hooping comes together in the brain. Physical activities that involve the coordinated use of multiple body segments aren’t simple at all. In 2004, Biological Cybernetics published a 15 page study examining exactly how human beings hula hooped and came to the conclusion that a great deal of the action comes down to concurrent oscillatory motion of the hips, knees and ankles [source: Balasubramaniam and Turvey]. And yet, it’s a little more complicated than that as well.

In a 2008 edition of the journal Human Movement Science, which seems like something we’d all want to read, they added to the equation that while all hoopers employ the same basic movement to maintain the hoop’s rotation, the contribution from the hips, knees and ankles varied from person to person [source: Cluff et al]. In other words, an individual’s personal style and inner rhythm factor heavily into successful hooping, but then we all see that for ourselves on a regular basis. What works for one person doesn’t always work exactly for another, which is one of the reasons hooping is so dynamically individual and exciting. When we discover just what is required to become the axis point in the center of our own personal circular plastic universe, it just doesn’t get any cooler than that!

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Philo Hagen Philo Hagen is the Co-founder and Managing Editor of Hooping.org. He’s been spinning things up online and off since April 2003. Co-Founder of the Bay Area Hoopers and LA Hoopers hoop groups, Philo has performed internationally and has won Hoopie Awards for Male Hooper of the Year and Video of the Year. He lives in Los Angeles, California, USA.

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.

The Hooper Versus Gravity

Falling Apple [This week Hooping.org columnist Lara Eastburn takes on gravity and wins.]

by Lara Eastburn

“I just can’t keep it up.” Anyone that’s handed a hoop to enough first-time hoopers has encountered this objection at least once. And sure enough, as they demonstrate for you, they will give that baby a nice good spin, and watch defiantly as it wobbles, with much fanfare, to the ground. So we begin to eliminate the most possible offenders — a bulky jacket or cell phone, a big ol’ Texan belt buckle — while switching out the “problem” hoop with a bigger one, enthusiastically encouraging our new friend to give it another go. Hoop is touching the back of the waist, check. Hoop is on a good, flat plane, check. Now, go! The abundant and hopeful circle orbits twice, maybe three times, then crashes and burns. Aaack! You’ve got maybe 30 seconds to problem-solve, or your new prodigy may give up forever. Panic. Your ‘everybody can hoop!’ mantra is on thin ice. Or is it? What’s going on?!