There is a magical boulder weighing about 5 tons in Shizhu County. As long as a finger touches its itch, it will keep shaking. Why?

There is a 5-ton "ticklish" boulder in Shizhu County, Chongqing. As long as you touch it gently, the boulder will shake from side to side and giggle. According to local legend, this stone is Lu Ban's masterpiece. After repeated inspection, experts believe that this stone is "ticklish" because of mechanical reasons. Are stones really ticklish? Maybe it's a record! On February 30th last year, at 65438+, Luo Lailin, a geological expert from the School of Geographical Sciences of Chongqing Normal University, rushed to Baiyanba Formation in Jiumang Village, Xinle Township, Shizhu with full doubts. The boulder called "tickling stone" by the locals is located in the rock bay (small place name) of this group.

The stone is about 2 cubic meters and weighs about 5 tons. It is an irregular polyhedron with a large number of turtle cracks and pits. It "grows" on a cylindrical stone exposed from the ground, with a joint of about half a square meter. "It's really ticklish like people! Tan Mingwan, deputy head of Xinle Township, gave a live demonstration: He put his finger in a small eye ("tickling point") on the "tickling stone", and when he touched it gently, the boulder swayed from side to side and giggled. Without touching the "ticklish point", five or six adults tried their best to push the boulder, and no matter which angle they changed, it did not move. Liao Dashun, a 72-year-old villager, said that many local people have seen the strange phenomenon of this stone. Some people even tried to pry it with a steel drill, but failed.

What's the reason? Luo Lailin gave the answer after repeated investigations and experiments. He said that this stone belongs to the calcium carbonate rock among sedimentary rocks, which was formed about 500 million years ago. Judging from the turtle crack on its body, this "ticklish stone" was originally "long" on a nearby cliff, and fell off the cliff under the action of geological movement and weathering, just landing on the cornerstone below, and turned over in the process of falling. It does not belong to the common pneumatic stone in nature.

The reason why it can only be pushed at the "itchy point" and can't be pushed anywhere else is because the stone is heavy and has high friction, which is of course not easy to push. The contact surface between the tickling stone and the lower cornerstone is a long strip, and its moment, that is, the arm of force generated by gravity, is fixed. To make the "ticklish stone" move, the applied torque is greater than the torque generated by the gravity of the stone, and the longer the torque, the more labor-saving. The "tickling point" on the "tickling stone" is at the longest position of the arm of force, so it is natural to move the stone with little force. The arm at other angles is relatively short, so it can't be pushed naturally.