The physics of FOOSH

So at the moment I am teaching about momentum and impulse in my physics class. I really like these topics because they have so many real life applications that are easy for students to see. I’ve talked about car crashes, air bags, and crumple zones. I love bringing in a variety of different sports from karate to archery to mountain biking. It is such a tangible topic, even if the math with all its trigonometry can cause some challenges.

It got me thinking though, how did physics play into my breaking my arm?

A FOOSH is fallen on outstretched hand. That’s the term they use at the hospitals. By the way, this again links back to being able to speak the lingo, cause I went into the doctor saying I FOOSHED and they understood exactly what I meant. So why is it that a FOOSH is important enough to have its very own acronym? Physics.

The force it takes to break a bone or damage soft tissue varies with many different factors including angles, density, etc. However, falling or landing on any part of your body does cause an impact, or if you will, an impulse. An impulse is just a change in momentum. So when I crashed my bike I went from having some amount of momentum based on the mass of me and my bike and my speed (velocity) to having zero momentum as I ran into the pavement.

The impulse is determined by the force and the time. In other words, how much time and force did it take to stop my movement. An airbag decreases the force you experience during a car crash by increasing the time it takes your body to stop. This is why there are fewer injuries, or at least less serious ones. When you were taught to land a jump you were probably told to bend your knees. As you bend your knees you increase the amount of time it takes to stop your momentum, which decreases the force. Think of how much it can hurt if you hit a step before you were expecting it. Typically, it hurts because your knee didn’t bend so you experienced a greater force over a shorter amount of time. I actually know someone who stepped of the bus and shattered his leg because his leg wasn’t able to bend and increase the time it took to stop.

The same thing happens with a FOOSH. My elbow was locked when I hit the ground. As a result, it couldn’t bend to increase the time it took my body to stop. This meant that I experienced a greater force and that force went through my bones and soft tissue causing the fracture and some additional damage.

When I teach adult skating classes I always make the skaters practice falling. You can imagine that it isn’t their favourite thing to do. But they need to be comfortable with falling. The more comfortable you are, the less likely you are to tense up. This is why kids can typically fall without getting injured: they turn to jelly. They’re relaxed when they fall, which keeps their muscles looser, and they are able to “absorb” more of the impact. This basically just means that it takes them more time before they come to a complete stop.

Right after I broke my wrist, I had someone tell me that I need to learn how to fall properly so that I don’t get injured. I was a figure skater, I’m pretty good at falling. But having the stress of the car about to hit me and the complication of the bike underneath me, meant that most everything I know about falling went out the window. As a result, my wrist experienced too great a force and I ended up injured.