Impact Physics 101: how impacts work, and how protectors prevent injury.

Today we’re talking about the physics behind an impact.When practicing sports, we all use paddings and rigid protectors... but do you actually know WHY they work? You can also check this same article in video format at our YouTube podcast https://youtu.be/3JcbHcI-Y8U

To make it as simple as possible, an impact exerts a force by transferring its energy onto an impact surface. The harder the impact, the higher the energy. The smaller the impact surface, the more concentrated that energy is. So, how do we protect form that? Let’s begin from padding: padding is a soft layer interposed between your body and the impactor. This layer makes contact with the impactor in advance and, as it progressively compresses, incrementally transfers energy to your body. Since the total energy of the impact is the same, but the time it takes to transfer it to your body is stretched out, less force is exerted at any given time. So, we could say that the lower the transmitted force, the lower the risk of injury. But then, what about rigid protectors? The smaller the impact area, the higher the concentration of the force in each point will be. The amount of force exerted over a certain area is called pressure. So, we can rephrase our initial sentence once again: the lower the impactor’s pressure is at any given point during an impact, the lower the risk of injury. This is the reason why rigid armor is so tremendously effective! It fundamentally acts as an intermediate impactor: it takes the hit, and transfers it to the body on a much larger surface. To put this in perspective, if the time to stop the impactor increases from one millisecond to just ten milliseconds, reducing the transmitted force by ten times, and the impact area increases from one square millimeter to one square centimeter, which is a hundred times bigger (ten times longer by ten times wider), that is one tenth of the transmitted force, spread on a hundred times the area, so the pressure is divided by a thousand!

This is the reason why combining a rigid plate over a padding layer has been the go-to solution for hundreds, or even thousands, of years. It’s cheap, effective, and relatively easy to attain.