Cranking the numbers provides me 1,394 nails—which is definitely not that many. A 40-by-40 sq. grid is 1,600 nails, and that is greater than it is advisable to stop a pores and skin puncture.
So, what for those who substitute the nails with a bunch of damaged glass? It’s actually the identical factor. Positive, glass is likely to be sharper than nails, but it surely additionally has some flat components. So long as the contact space is giant sufficient, the glass received’t harm anybody.
In order that’s the key: It would not take robust pores and skin, just a few physics.
Smashing Rocks, Mass, and Acceleration
Now, let’s transfer on to the a part of the demonstration when a soldier smashes a rock on prime of the dude’s chest as he lies on the mattress of nails. The important thing physics lesson right here entails Newton’s second regulation. It is a relationship between the web drive on an object (Finternet), the mass of the article (m), and the article’s acceleration (a). If the article is constrained to solely transfer in a single dimension (to make issues simpler), then we are able to characterize this as the next equation:
The acceleration of an object tells you the way that object’s velocity adjustments. So, if the factor is simply staying nonetheless, then the rate will consistently be zero, which might be a zero acceleration. Nevertheless, even when the article is shifting, it could actually have a zero acceleration so long as its velocity would not change. If the article is growing in pace, then it will have a constructive worth for the acceleration. That signifies that when an object slows down, it has a adverse acceleration. (Word: This assumes movement in a single dimension.)
Right here’s an instance: Suppose two individuals are every standing on a skateboard. (These are zero-friction skateboards—you could find them on the physics retailer.) On one board is an grownup with a mass of 80 kilograms, and on the opposite is a baby with a mass of 40 kilograms. If I push on the grownup with a drive of 80 newtons, it would present an acceleration of 1 meter per second per second (1 m/s2). If I push with this identical drive on the kid, the acceleration shall be twice as a lot (2 m/s2), because the child’s mass is half that of the grownup.
