(upbeat music) – This is a five acre covered test track at the VRC. Engineers design structures like this against failure by understanding how the stress forces are applied to the structure. This structure can withstand 20 inches of snow, and up to 90 mile per hour winds. Wow, what a structure! The human body is an amazing structure, too. To help prevent crash injuries to our structure, scientists and engineers study how stress forces can affect tissues and organs during a crash. Did you know the strength of our tissues and organs can vary depending upon how the forces are applied, and the condition of the tissue or organ. Let’s take a quick look at three general examples of how injuries can occur. In this example, the string represents certain types of tissue in your body. Right now it’s under very little stress. Watch what happens when I try to cut it. Nothing. But if I put some additional stress on it, when I try to pick up this weight, then I try to cut it, look at that. So, certain types of tissue in your body, if they’re under additional stress, they’re more prone to failure or injury. In this example, the balloon represents certain types of tissues and organs that are stretched in all directions. In the string example it was stretched in one direction. What do you think’s gonna happen if I try to push this needle through the balloon? All right, watch carefully. Whoa! No pop. Hang on, I’m not done. Wow, check it out! No failure, no rupture, no injury. Okay, keep watching. All right, now watch. (balloon pops) Failure, injury. So what was the difference? Well if you’re watching really closely, you notice exactly where I put that needle. So, let me ask you this. Where do you think the balloon is stretched the tightest? On the sides, top, bottom? It’s actually the sides, stretched in all different directions. Stretched the least at the top and the bottom. So if you’re looking closely you can see that’s where I put the needle, where the balloon was a little bit darker. That means that little area the balloon wasn’t stretched as tightly there, or on this end either. So, in tissues and organs the same sort of thing happens. If it’s stretched really tightly in all different directions, it’s more likely to rupture or fail and cause injury. Please don’t try this at home. This time, we’re gonna do something a little different. Another type of injury is called blunt force trauma. What do you think is gonna happen to this bottle when it experiences a blunt force trauma? Ready? (glass shatters) Wow! How’d that happen? Well, when I hit the bottle with the rubber mallet, I actually forced the bottle down quickly, ahead of the bulk of the water, creating a cavity. Then the water rushed into that cavity and blew out the bottom of the bottle. Now, something else really happened in that cavity. Since it’s an area of really low pressure, it actually vaporized some of the water molecules to form tiny bubbles, that’s known as cavitation. Something similar happens to certain types of tissues and organs in your body during a blunt force trauma. The blunt force actually creates a pressure wave, stress wave, or shock wave that travels through your tissues and organs creating these different areas of high and low pressure. In the areas of low pressure, cavitation can occur. Some researchers suspect that these tiny bubbles are actually responsible for certain types of traumatic brain injury. Interesting, huh?