Light as a feather
Santa Claus is still heaving the presents in the sack onto his back. It couldn't be more archaic. Then one of these frame backpacks is better - or even better: one with new bungee technology. This reduces the energy expenditure with each step.
It is well known that everyone has to carry their parcel. One heavy, the other light. What they all have in common, however, is that it always rocks quite a bit when you walk. The movements of the hips lift every backpack and everything else strapped to your back several centimeters with every step.
The problem: Exactly when both feet touch the ground, the backpack has to be pushed up again - its apparent weight sometimes doubles at the peak load. But it is precisely in this phase that the most energy is released to the ground. Therefore, the "reduced" weight at the top dead center of the up-and-down movement cannot compensate for the additional expenditure of energy. In practical terms, this means that backpacks seem heavier once you start walking with them. When running, the effect is even worse.
Larry Rome from the University of Pennsylvania has now come up with a solution to this. His suggestion: If the actual load is hung sufficiently flexibly and the constant ups and downs are fought, the effect should not materialize. In the frame of a conventional backpack, he therefore attached a movable plate to two rubber "bungee cords" on which it could move freely up and down. This plate in turn carried the backpack bag with the load - that is: the gifts.
If you start walking with the construction on your back, the plate and load begin to swing up and down - but only in relation to the rest of the backpack. Because the phases of both movements are shifted almost exactly against each other, they balance each other out in the end. Viewed in absolute terms, the backpack bag appears to almost float in place while people move around the bag, as video footage shows.
In order to be able to prove mathematically that his new carrying device can put all other models in the sack, Rome measured the resulting forces and the energy expenditure in an experiment: The swinging backpack actually reduces the acceleration forces in the up and down Movement by up to 82 percent. "It's like getting an extra 5 kilograms 'for free'"
(Larry Rome) With the same energy it takes to move 22 kilograms in a conventional backpack, Rome's construction carries a full 27 kilograms. "It's like getting an extra 5 kilograms 'for free'," says the inventor.
If the load is too light or too heavy, the wearer must of course readjust the length of the elastic cords so that the plate does not hit the top or bottom and the benefit of the construction would be lost - not to mention the lack of carrying comfort. How this is basically ordered can probably only be answered by those who have already had the opportunity to try out the device. The problem of the bag swinging back and forth uncontrollably on the back, as with elastic shoulder straps, should at least not occur.
But whether conventional carrying concepts will actually be able to pack up in the near future will only be seen in practical tests. In any case, the inventor has fewer people in mind like St. Nicholas, who can already flexibly distribute his load of presents to Knecht Ruprecht, but rather people who carry heavy weights for their job and often have to run - paramedics or soldiers, for example. Even school children, whose stuffed satchels sometimes lead to orthopedic problems, could benefit from it. Rome intends to market the invention, which has already been patented, with his own company.
By the way, the seesaw backpack is said to have its forerunner in the springy bamboo carrying frames of Asian traders. It seems as if the Far East has once again been quicker to invent – just like with pasta, paper or porcelain. And that although there is actually no Santa Claus there.