With every trauma call we run, there are two things that are almost absolute certainties. And I don’t mean that in the tongue-in-cheek sense, like, “We are certain that the elderly fall victim will live on the third floor and the elevator will be broken or nonexistent.” or, ”We are certain that the nursing home C.N.A. will call for that extended inter-facility transfer 12 minutes before the end of our shift.” type of certainty. I mean…even more certain than that.
When people call us for trauma, these two things are certain.
1.) Two objects collided with each other.
2.) Someone called 911.
When we put these two certainties together, we can make some fair assumptions about trauma calls. Objects colliding with each other aren’t such a big deal. It happens all the time. If my fingers weren’t colliding with the keys on my computer keyboard, you wouldn’t be reading this right now. But nobody’s running off to call 911.
It’s the second certainty that gives us pause. You see, people don’t start activating 911 until things collide in uncontrolled ways. Trauma calls happen when things collide together in unexpected ways and with unexpected velocity. It’s as simple as that. Now that I’ve said that, it sounds so profound that I want to write it down again and put my name under it. Here:
“Trauma calls happen when things collide together in unexpected ways and with unexpected velocity.”
- Steve Whitehead
Doesn’t it sound more profound in quotes? I agree. …Lets move on.
As obvious as it sounds, it bears repeating for one simple reason. If all of our trauma calls originate with two or more objects colliding with each other, doesn’t it make sense to spend a little time learning the nature of how objects in our universe behave when they collide with each other? Regardless of what two objects collide, whether it be Grandma Smiths hip and her linoleum floor or a minivan and an SUV, there are some elements that are always true about the way things collide. When we understand them, we can better predict the potential for damage.
Warning: Math Equations Ahead
No…wait, where are you going? Come back. You can do this. You’ll thank me later.
So what do we mean when we say kinetic energy? We toss that phrase around a lot when we talk about trauma. When we talk about kinetic energy, we are referring to the amount of energy a moving body is carrying around with it.
If something is standing still, it requires energy to get it moving. that energy is carried by the moving object until it stops. To stop, that energy needs to go somewhere else. It needs to be transferred to another body or converted to another type of energy. (Like heat for instance.)
All of this happens because of four basic laws of motion.
1) Newton’s first law of motion. A body in motion or at rest will remain in that state until it is acted upon by an outside force. So if something is still, it stays still until something moves it. If something is moving, it will keep moving until something stops it. Gravity and friction count as somethings. So does an 18 wheeler.
2) The law of conservation of energy. Energy is never created or destroyed, it only changes form. So once something is carrying around all that kinetic energy in the form of mechanical energy, that energy has to go somewhere before the thing can stop. Primarily, it’s going to be transferred to another object or become heat, also known as thermal energy. (Think about vehicle brake pads.)
3) Newton’s second law of motion. Force (f) equals mass (m) multiplied by acceleration (A) or deceleration (D). That looks like this:
f = m X A or f = m X D
Lets look at one last law and then talk about what all these equations mean to us when we’re trying to predict the potential for damage or injury.
4) The law of kinetic energy. Kinetic energy (KE) always equals one half the mass (m) multiplied by velocity squared. For you visual folks, this one looks like this:
KE = 1/2m X v^2
If we want to figure out how much energy is moving around with an object, we need to find out how much it weighs and divide that weight by two. Then we need to figure out how fast the thing is moving and multiply the speed by itself. Then we need to multiply those two numbers together. It’s easy. You can do it with a hand calculator.
What we see when we start playing with the numbers is that, when we’re talking about moving energy, speed means way more than weight. Speed has a dramatic and exponential affect on the energy carried by moving bodies.Here’s an example.
Let’s say you’re driving around at 30 MPH in a Toyota Sienna. Strait off the dealers floor, it’s going to weigh about 5,600 pounds. (A quick apology to the entire metric-using world…this is an American blog.) Our kinetic energy equation is going to look like this:
KE= 2/5,600 X (30 X 30) or KE = 2800 X 900 or KE = 2,520,000
So our Toyota is carrying around some energy for sure. 2,520,000 units of kinetic energy is about 84,000 foot pounds of force that all need to go somewhere when our Toyota hits a tree or a parked school bus. Now let’s try the equation two more times. First let’s double the vehicles weight, then let’s double its speed.
OK, let’s switch out of the Toyota and try a Dodge Ram 3500. This baby comes off the showroom floor at a whopping 11,000+ pounds. Now our equation looks like this:
KE = 2/11,000 X (30 X 30) or KE = 5,500 X 900 or KE = 4,950,000
Good to know. We almost doubled our vehicle weight and we also almost doubled our amount of kinetic energy. So vehicle weight has a constant effect on kinetic energy. Twice as much weight means twice as much energy to absorb or disburse.
Now let’s get back in our Toyota and double the speed. Our equation is going to look like this:
KE = 2/5,600 X (60 X 60) or KE = 2800 X 3600 or KE = 10,080,000
Wow. For the record, that is exactly four times the kinetic energy. So, for every time we double an objects weight, we get a proportional doubling of the kinetic energy moving around. For every time we double the same objects speed we get four times the amount of kinetic energy moving around.
For the record, our Dodge Ram traveling at 60 MPH would be carrying 20,160,000 units of kinetic energy or 673,000 foot pounds of force. That’s 8 times more energy than the Toyota Sienna had at 30 miles per hour.
What does all this mean to us? It means that weight is important, but speed really is king. Consider how much the moving object weighs, but really pay attention to how fast it was traveling. The same is true for falling people or objects that fall on people. How much the falling object weighs is important. How far it fell is very important.
This also applies to people. A 180 pound man who strikes his steering wheel at 30 miles per hour will have to absorb 81,000 units of kinetic energy with his body. The same man traveling 60 miles per hour will need to absorb 324,000 of those units. That could make for two very different calls.
This is definitely something worth keeping in mind as we consider the three collision rule. What is the three collision rule you ask? We’ll talk about that next.
(Author Addendum: In this post, “units of kinetic energy” is an arbitrary quantity used to demonstrate the relationship between the several examples offered. To calculate true kinetic energy in a usable form like joules, you would need to do several conversions prior to calculating.)
What do you think?: Does an understanding of kinetic energy help you evaluate your trauma patient? How much attention do you pay to the forces involved in a traumatic incident?
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