Crash: Seatbelts, Airbags, and the Science of Safety

Accidents happen, that’s a fact of life. There are countless things we can predict. There are countless things we can’t, especially when it comes to people and how they react in times of shock, surprise, or crisis.

There is one thing we can always do, though. Learn.

Learning from the past, accidents, things that happened that no one knew would, that’s what we do best. We can use physics and science to understand why things happened the way they did and make predictions about how to prevent them from happening again. Can we always stop tragedy from happening? Absolutely not. Some things are just too unpredictable. What we can do is help make things safer and protect people from more harm than there might be otherwise. Safety is a science.

Newton’s 1st Law says that something moving is going to keep on moving until something (an unbalanced force) stops it or changes its motion somehow.

Imagine being on a roller coaster. As it goes over the first drop, you feel your insides lift in your body and you’re pinned to the back of your seat. Then, a few seconds later, that feeling inside goes away and you find you can lean forward.


It’s the same thing when a plane is taking off, or a car is accelerating super quick!

It’s all about inertia. All things resist a change in their position, at least at first, depending on the size of their mass.

You are a separate thing from the roller coaster, the plane, or the car. When they change position, it takes a moment for the forces that be to start acting on you and for your body to change position too!

Thing is, this isn’t only about speeding up. It’s about slowing down, sometimes really, really quickly.

Let’s say there is a car traveling 60 km/h. Maybe it’s a cartoon world and there’s a brick wall up ahead painted to look like the road and the car slams into it head-on. The front end of the car crumples like a soda can and the car comes to a complete stop in the span of 0.1 seconds.

What happens to the driver? The car was stopped by an unbalanced force. The person was not…yet.


They will keep traveling that same velocity until something stops them. It may be the windshield or the wall. Either way, they’re going to decelerate just as fast as the car did, and a human is a lot more fragile than a giant hunk of metal.

But what if there was something to slow the drivers velocity? That’s exactly what a seatbelt does.

Half of all people who die in car crashes would have survived if they’d been wearing a seatbelt. In the US, there are 37,000 traffic accident related deaths per year with an average of 101 per day. 50 people per day could be saved by seatbelts. Unfortunately, nothing can bring those people back, but we can learn from the tragedy. of course, thousands more crashes and injuries happen per year and countless injuries could be prevented or minimized by seat belts, too.

The amount of force needed to slow a person’s speed from roughly 60 km/h it so ends up being nearly 14 times the force of gravity. That’s why Seay belts loosen before tightening. They are meant to slow the person down over a longer period of time, meaning their change in velocity happens over a longer time. Their acceleration is slowed, therefore the force acting on them is lessened too.

F=m x a

That’s Newton’s 2nd Law!

Of course, seatbelts aren’t the only safety tool in cars.

Air bags are actually super sciencey.

Obviously they are a big cushion, right? But, the way the work is that when a collision occurs a chemical reaction happens within the bag that produces nitrogen gas, quickly inflating the bag to slow the driver’s acceleration just like the seatbelt, but they also then release that gas through tiny little holes so that the bag the driver is hitting isn’t just another hard object.

Have you ever had an air mattress? Maybe a pool floaty? If you jump on them it’s a lot like jumping in the ground. There’s nowhere for the air inside to move to so you might as well be landing in a solid. But if you open up the air escape valve and jump on top to help it drain so you can put it away, it’s a much more cushioned landing. You slow down pretty quick and then slowly ease towards the ground. Same concept!

In the end, the message is simply this: safety is a science. These things exist for a reason. Seatbelts save lives. Who knows, someday it may be your life they save.

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