How Is The Deadlift Like A Cobra Daytona Coupe?
This article is a very technical article and I posted it knowing this. If you are a geek about details, you will love it! For those of you who want to dig in we will appreciate your comments! Thanks to – Mary Boudreau Conover and her husband Ed, two brilliant minds helping us understand the specifics of physics and the deadlift! -Eva T.
Here’s the Cobra
Notice the length of the car and find its center. That’s where its engine, the heavy part of the car, sits ─ dead center between the front and back wheels and right in front of the driver. With the heavy part at its center and the lighter parts at either end, a low polar moment of inertia exists, improving the cornering and giving the driver better control in a more responsive vehicle because there is less inertia to overcome.
The Formula 1 Racing Car
This car achieves a low polar moment of inertia by having the driver centered and forward with the engine behind the driver. These cars are built light so that ballast can be added to achieve the balance and responsiveness that comes with perfect low polar moment of inertia.
The Novice Deadlifter and the Cobra Daytona Coupe
The weight distribution in the light deadlift is like that of the Cobra. The heaviest portion of the lift is the bar with lighter weights on either end. The axis passes vertically through the center of the bar so that there is the potential for twisting around that axis. This defines a low polar moment of inertia, so the car and the bar are more responsive to small corrections by the Cobra driver and the novice deadlifter. As soon as you start adding more than 15 lbs to the 15 lb bar or 20 lbs to a 20 lb bar, you are about to cross the line into a little higher polar moment of inertia. For example, there will be a difference in control between a 15 lb bar with 50 lbs of plates and a 45 lb bar with 20 lbs of plates, even though both set-ups are the same total weight. The novice lifter will very quickly be capable of a 55-65 lb deadlift. In the interest of more control, let them use the 45 lb bar with the 5 lb plates as soon as possible. There’s no reason to keep loading that light bar when they’re lifting heavy enough to switch up to the 45 lb bar. By the time the lifter’s progress has required plates heavier than the bar (a high polar moment of inertia), the lifter will be strong, steady and in control.
The Fly Wheel, High Wire Walker and the Heavy Deadlift
When the mass of an object is distributed far from its axis of rotation, as seen here as part of the Boulton-Watt steam engine, it has, by design, a high polar moment of inertia so that it easily spins around smoothly when mounted on the crank shaft and driven by a motor.
High wire walkers want their bar to be long and heavy enough for a high polar moment of inertia. This is 68 year old Jay Cochrane crossing over the Niagra Falls with joy, grace, balance and showmanship (July 2012). He walked the quarter mile from the top of Skylon Tower to the Hilton Fallsville Hotel at a height of about 600 feet above the ground without a tether or a safety net. And he did it every day of the summer 2012.
This heavily loaded bar can be compared to the fly wheel and the wire walker. In all cases there is a high polar moment of inertia. In this case the 45 lb bar is the lighter weight; the heavy weights are at a distance from the vertical axis at the center of the bar, resulting in the high degree of inertia. This very strong man, lifting 825 lbs., will tell you that he has felt no instability during the lift, in spite of the inertia and the unintentional fact that the load itself is unbalanced with the plates at his right being lower than those on his left ─ whew! No worries, his strength is in control, but if the bar moves because it has been “acted on by an unbalanced force” it will continue to move and be very hard to control because of its high degree of inertia. (Newton’s first law of motion).
- Moment. The distance between an applied force and the fulcrum (pivot or axis) in the lever system, very nicely illustrated and explained in Rippetoe’s third edition of “Starting Strength.”
- Inertia. Resistance to change. Objects that need applied force to move them, stop them or change their direction ─ Sir Isaac Newton’s first law of motion.
- Polar moment of inertia (aka “moment of inertia”). A property involving a rigid mass and the torque needed to rotate it around an axis. With a larger moment of inertia more torque is needed to increase the rotation of that mass, or to stop it. Moment of inertia depends on the amount and distribution of the mass of the object and is often optimized to achieve specific results. The guy who is building his own race car would be thinking of how to improve the handling of his vehicle regarding its ability to turn when influenced by the torque provided by the steering wheels (You want a low moment of inertia around a vertical axis for a race car).
A personal “moment”. I am not a student of Physics, although I view it as one of the most useful of all available subjects in the lifetime process of learning, supporting as it does, so many other subjects, activities, and academic disciplines. So, I am grateful to my husband for his offhand comment about the “Cobra race car and its low polar moment of inertia”, causing me to compare it to ─ what else? The early phases of deadlift training! Long ago, at the beginning of my career as an author and teacher of electrocardiography, it was my husband who helped me understand the cellular electrophysiology of the heart. I no longer hold ECG seminars nor write books, so this simple article, that has so much to do with physics and Newton’s law of inertia, is an opportunity to acknowledge this brilliant man’s role, not only in my life and that of our children, but in the defense of our country during the very tense time of the Cold War, when the frightening threat of a nuclear attack coming in over the North Pole from Stalin’s Soviet Union was very real.
Edward L Conover II, BSEE, Aerospace Engineer and Cold War warrior. It is difficult to describe the breadth and depth of Ed’s knowledge of all things that move, electrical and mechanical: the Phoenix missal and radar; shots to the moon and reentry; atomic bombs and atomic power; computers, engines, chemistry, X-rays and math; race cars, high wire walkers, rapidly spinning ice skaters and fly wheels; construction, metal work, structural integrity and the physics of it all.
Mark Rippetoe, brilliant author, experienced, respected, caring and generous coach of weightlifters, athletes, and all who want to be strong. Thank you, Rip, for reviewing this manuscript, again and again as I sorted it all out, encouraging me to supply a glossary and especially for describing to me what it feels like to deadlift 700 lbs and more. Steady and solid ─ that would be you.
Mary Boudreau Conover