Pretty much everyone agrees that distracted driving is bad. And the most common distraction just might be your phone. People seem convinced that they must see that notification or status update right now. This can cause problems when you’re driving. You know, crash problems.
Now, you may be saying, “Wait. Aren’t you a physicist? What does distracted driving have to do with physics?” Well, everything in life gets back to physics. Including this. Let me explain.
A Simple Velocity Problem
So there you are, driving to school or work or whatever when your phone buzzes. “I’ll just look at my phone for one second,” you think. “It will only be a second and I should be fine—right?” Wrong.
Let’s say you are traveling at some speed v and you take just one second to glance at your phone. That is one second that you are not looking at the road. What happens during that one second? First, let me define average velocity (in one dimension—I add that because I hate being technically wrong).
In this definition, Δx represents the change in position and Δt represents the time interval. Please stop saying velocity is distance over time—that is only sometimes true. In this case, I know the time interval is one second. If I solve this equation for the change in position, I get:
If the velocity is very small, the distance traveled in one second also is very small. OK, how about some values: Say you’re creeping along at just 1 m/s or 2.2 mph or 3.6 kilometers per hour. You travel 1 meter in one second. (No, I’m not going to convert that to feet. You just get in the habit of using metric units—the rest of the world long ago realized this is the best set of units.) But if you’re zipping along at, say, 25 m/s (56 mph, 90 kph) then you travel 25 meters in one second. That’s about one fourth of a football field or about two school buses. A lot can happen in that kind of distance.
Now imagine the time spent reading a text, or a tweet, or someone’s Facebook status. Every second you spend staring at your phone instead of the road is another 25 meters you’ve traveled while not paying attention. And it’s not just the time spent moving that matters—there’s also the time required to react to anything that might happen.
That might seem like common sense, but it bears repeating for perspective. Yes, many things can distract you for one second (eating, changing the radio station, reading a map, sneezing, thinking about physics). None of those is any better than glancing at your phone.
What About Traffic Lights?
I can hear you saying, “I am not the problem. I only glance at my phone at stoplights.” Sorry. You are the problem, too. Why? Because you are backing things up for everyone else.
Let me paint a picture. There you are, driving to school or work or whatever and the light turns red. You stop behind a ton of cars. The light turns green and cars start to move through the intersection. You are getting fairly close to the light and BOOM—the light turns yellow, then red. You didn’t make it. I guess you will have to wait—oh, you can play on your phone.
Ah. But you are distracted. Which means you aren’t paying attention. The light turns green, and the guy at the front of the line proceeds through the intersection. Then the next car. And so on. Suppose each driver has a reaction time of one second and needs another second to start moving. If the green light lasts 60 seconds, that means 30 cars move forward and maybe 20 of them get through the light. No one is angry.
If people are looking at their phones instead of the light, their reaction times increase. Let’s say they need two seconds to react and one second to start moving. During that same 60 second green light, just 20 cars start moving and maybe 15 make it through the light. That leaves five people who must sit through another red light because other people felt the need to check their phones.
Just put down the phone. Stick it in your pocket or purse or the glovebox. I like to think of myself as a pilot, not a driver. My number one job is to safely pilot my vehicle. That’s your number one job, too.
Written by Rhett Allain / Wired