## Blindsided

Cars today come with all sorts of crazy bells and whistles designed in the name of safety. There are backup cameras, blind spot monitors, and even sensors that will tell you when you're drifting out of your lane! But are these technologies making us that much safer, or are they just enabling us to drive carelessly?

Let's take your mirrors, for example. With all of this newfangled technology, it's easy to forget to adjust your rear- and side-view mirrors before starting the car, and trust that the car will tell you when something is wrong. But what if you drive a car that doesn't have technology like blind spot mirrors, or the technology itself malfunctions? Knowing how to adjust your mirrors seems like a pretty important (and potentially life-saving) skill.

So, how can you be sure that you've got your mirrors in the right positions?  Despite the importance of this skill, a lot of people adjust their mirrors incorrectly! In case you aren't a maven of mirror mechanics, let's explore how people typically set their mirrors (and how they ought to set them).

The rear-view mirror is fairly straightforward: you just need to adjust it so that you can see what's happening behind you.  Do you think the mirror in the interactive diagram below is adjusted properly?   Play around with it by dragging the mirror's rightmost point until you're satisfied.

(Note: when light hits a mirror, it's reflected across a line perpendicular to the mirror's surface.  This is known as the law of reflection, and is how the region in the diagram below is created.  You can use the buttons to hide and show those perpendiculars, if you're so inclined.  No pressure, though.)

What about the side-view mirrors?  Here's where we start running into problems. A fairly common technique is to adjust them so that you can see just a sliver of your car in the mirror as you drive.  This gives you a handy point-of-reference when you're looking into the mirror: if you know where your car is, you know where everything else is by way of comparison.

Unfortunately, this technique creates some pretty serious blind spots — areas that the driver can't see — on either side of the car.  Focusing just on the passenger's side mirror, you can see in the diagram below that when the mirror is positioned so that you see part of your own car, the side-view mirror overlaps significantly with what you can already see in the rear-view mirror!  And since the side-view mirror is supposed to show, you know, a side view, maybe this technique is less than ideal.

Thankfully, though, there's a better approach. Explaining it in words is a little cumbersome, but this video does a pretty good job describing how it works:

Basically, to adjust your driver's side mirror, you should lean your head all the way to the left, then push the mirror out until you can just barely see your car.  For the passenger's side mirror, you should learn towards the center of the car, and again, push the mirror out until you can just barely see your car.  That way, when you're sitting normally in the driver's seat, you won't see any of your car in the side-view mirrors, but you will see much more of the road on either side of you.

What do you think? Based on the interactive diagram below, does this technique eliminate blind spots? And how does this compare to having your car beep at you when you drive erratically?

Teachers: want to talk to your students about congruent angles, reflections, and blind spots?  Then check out our featured lesson, Blindsided.