How protective equipment decreases the force of impact

The goal of protective equipment is to decrease the force imparted on the person wearing it. Whether you are getting tackled in football, or are in a car accident, a great deal of force is applied to you. Injuries occur when this force is imparted on your body, as we are not designed to accept such impacts. Protective equipment acts to either divert the force away from you, deform to absorb some of the energy from the collision and increase the time of impact and/or to spread the force of impact around an area, delocalizing it.

If our equipment deflects the impact great, that will reduce it. If it spreads the force around our body we will feel less of it in one spot, good again. But whenever there’s an impact, the energy imparted by the impact needs to go somewhere and that’s where we see the real benefit of protective equipment. The average tackle in the NFL provides 7117 Newton’s of force (1600 pounds). To explain the importance of reducing the force of impact we need to do some physics so hold onto your hat!

Consider the impulse equation → Ft = vfm – vim where F = force, t = time, vf = final velocity, vi = initial velocity and m = mass. The left side of the equation (Ft) is the force of impact times the time the impact lasts. The right side of the equation (vfm – vim) is telling you how much your velocity changes during the impact. The right side of the equation is fixed (think of traveling 5 m/s then stopping, it doesn’t matter how fast you stop, it’ll still have the same value). However, we can adjust the left side. Since the right side is a fixed number, if we increase “t” on the left, we would have to decrease “F”. This is good because it represents a decrease in impact force. That’s the key but how do we increase “t”? That’s where our equipment comes in. By deforming (squishing a material), the impact time increases a small amount (think 0.01 s vs. 0.02 s). This may not seem like much but a doubling of time (t) means a halving of force (F)! The more we can increase “t”, the less “F” will be. Airbags do this and so does the wall padding you might see in your school’s gym.