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Monday, February 1, 2010

Extra!! Extra!! Read all about it! Finally the secret behind the death-defying "Sphere of Fear" explained!

Have you ever been to a circus, amusement park, or stunt show? Well, all of those air defying and gravity smashing stunts are just good applications of physics and an understanding of motion. Not to say that these tricks are not dangerous and don’t risk life and limb, they do. However, the physics principles behind them are rather simple. Take for example the “Sphere of Fear,” “Globe of Death,” or “Circle of Doom” that is a staple in many circus acts. The stunt is fundamentally composed of a large spherical metal cage with one or more motorcycles and riders driving around on the inside. Created by Herb “Daredevil” Durkin after WWII, he and his wife believed that the public would pay good money in order to see the death defying “double loop.” For more than 30 years, they continuously added new tricks to their repertoire such as sidecars, more riders, and eventually, they decided to cut off the bottom half of the sphere in order to increase the risk and make it more exciting for the audiences. In the early 70s, Herb Durkin and his wife retired and left their “Sphere of Fear” to rust into scrap metal. From then on, fresh and innovative performers, entertainers, and daredevils have created similar acts and amazed audiences with their fearless acts of bravery.

Now onto the Physics!!!
Here is a “Prezi” that can explain everything: "The Sphere of Death" - Prezi
 In this "Prezi," you will find a description and analysis of the motion of the riders and motorcycles when riding in the "Sphere of Death." It includes a detailed description of both vertical and horizontal loops, what would happen if the riders go too fast, too slow, or just the right speed, and multiple FBDs and diagrams in order to help you understand what is the physics behind this amazing feat. To navigate the "Prezi," move the mouse to the bottom right of the "Prezi" and use the arrows to step forward or backward in the path.

Now that you know how it works, test you skills with the Homer Simpsons "The Ball of Death Game".

Black and Blue Colorful Fractal:
Blue and White Waves:
Dark and Gloomy Sphere of Death:
Green Sphere of Death in Motion:
Blurred Motorcycle in Motion:
Sphere of Death in Daylight:
Inside Sphere of Death:
Bright Colorful Blue Fractal:
Roller Coaster:
LED Circle:
Snail Cartoon:
Specific Tricks:
YouTube Long:
YouTube Short:
Homer Simpson Ball of Death Game:


  1. This is a great idea and the videos are an extra touch that finishes it off nicely. They relate nicely, but the "Prezi" is more of a video than an explaination. To enhance your project I suggest adding an explaination of what the video teaches. Then, students can "test their skills" in a fun game!

  2. Outstanding posting! You clearly answered your question with your FBDs and equations.
    The Prezi is well constructed as it first shows an example of the stunt through the YouTube video and then investigates the forces acting at various points on the sphere.
    I also like that you gave a neat introduction of this stunt in the posting.

  3. Perfect!
    yeah, I've got nothing to add.
    awesome job!

  4. Excellent. The media strip was awesome. Economy-wise, it was a little too much. Reduce the information and it would be perfect!

  5. Chris,

    Great videos and a truly cool subject. I really enjoyed it. I also like the fact that you wrote a lot of words to explain the equations. The nit-picky comment I would make is that, in the words, you sound a little unclear on what Centripetal Force is. Remember that F_c is the net force, the sum of the forces. It's not a "real force" on its own, it has to be provided by other objects outside of the motorcycle. And it isn't "overcome", either enough is there to keep the circular motion or not. Anyway, nice job. I didn't understand how to navigate the filmstrip at first, but once I did, I liked it a lot .


  6. Thanks to everyone so much for their thoughtful comments!! Mr. Reif, I understand your comment and how Fc is not a real force, but the net force that is acting on an object, and how Fc can be the right size and direction to keep the object in a certain circle or not. I knew that this might have been one of the problems with the diagrams that I utilized from the internet. Thank you so much for your input.