The "breaking a large stone on the chest" is a common and spectacular performance in acrobatic shows. It might be a slim lady lying flat on a long wooden bench with a large stone slab placed on her chest. At this moment, a burly man lifts a large hammer and smashes it towards the stone slab. "Dong..." After a few hammers, the large stone slab is broken. The slim lady stands up and waves to the audience, who are surprised to find that she is unharmed and breaks into thunderous applause. Even movie star Andy Lau has once performed the "breaking a large stone on the chest" under the attention of his fans.
The brilliance of this performance lies in the fact that the stone slab on the performer's chest breaks under the hammer's impact, but the performer remains unharmed. Why is that? Simply put, the hammer actually hits the large stone slab, not directly hitting the performer's chest. Moreover, there is usually a soft cushion between the stone slab and the performer, which allows the large stone slab to have a large contact area with the performer's body, so the impact force on each part of the contact surface is not large. For example, if a 30-kilogram iron ball falls freely from a height of 1.5 meters to the ground, the average pressure on the ground will reach dozens of times the weight of the iron ball. If the iron ball directly hits a person's chest, it will definitely cause injuries. But with a stone slab placed on the chest, the contact area between the stone slab and the body is hundreds or thousands of times larger than that of the iron ball hitting the ground directly. At this time, the force applied to each square centimeter of the performer's body is very small. Under the performer's preparedness, this evenly distributed force is not enough to harm the body. Calculations show that the heavier the stone slab is, the slower the speed of the hammer hitting the chest will be, and the more the performer can withstand the evenly distributed force acting slowly. Therefore, in the "breaking a large stone on the chest" performance, a slightly heavier stone slab is safer. Moreover, the soft cushion between the stone slab and the performer further reduces the pressure when being hit. Of course, non-professionals should not easily attempt this performance.