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6 Tiny Robotic Ants, Weighing 3.5 Oz. In Total, Pull a 3900-lb. Car (nytimes.com)
Reader schwit1 writes about MicroTug, a team of six microrobots that weigh just 3.5 ounces (99 grams), and can move a car: Researchers at Standford University's Biomimetics and Dexterous Manipulation Lab have developed six miniature robots that have the pulling-power to move objects 2,000 times of their own body weight. The tiny robots and their inter-coordination are based on that of ants. The microrobot uses a special kind of glue on its feet that make them serve as sticky gecko toes. "Their new demonstration is the functional equivalent of a team of six humans moving a weight equivalent to that of an Eiffel Tower and three Statues of Liberty," said David Christensen, a graduate student who is one of the authors of "Let's All Pull Together: Principles for Sharing Large Loads in Microrobot Teams paper. Researchers' fascination with gecko adhesive is nothing new. In 2010, Stanford mechanical engineer Mark Cutkosky developed a Stickybot that could climb walls. A
similar robot that could roll up on smooth as well rough surfaces was demonstrated by a group of researchers in Canada in 2011.
I was going to post something similar. I hate comparisons like these. The 'ants' are pulling against the rolling resistance of the car, not the car laying on its side, as would be the case with the tower equivalent weights. Unless you had some gigantic roller bearings to slide them across.
F=ma so if a is small then F, the force from the robots, can also be small. With over inflated tires and a smooth flat surface the rolling friction F needs to overcome can be quite small. Even a small child could push a 3900lb vehicle under the right circumstances. It would be far more useful (and less impressive to the masses) if an actual figure of force was given, much less any other relevant information.
I don't feel that was misleading. When somebody says that they towed their car, I do not assume that they put it on it's roof to do so.
And when they include the weight of the car in the statement, they are implying that the weight of the vehicle is somehow relevant.
The main hurdle to "pulling" something is the friction, not the mass. If you put the Eiffel Tower on a set of rollers that had the equivalent rolling resistance that a 3900 pound car has, I betcha six people could pull it, too. If the brakes aren't on, one person can push a loaded railroad car. And if you use levers and pulleys (machines) for assistance, you can pull a lot.
At many county fairs there used to be a popular show called "the tractor pull". People would compete in pulling a loaded sled with their tractors. They'd all start out able to pull the sled, but as the sled moved forward, so did a large weight that increased the friction between the sled and the ground. Only the beefier tractors could pull it the full distance, but all of them could pull it.
My personal favorites:
-SR