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Why Are Objects in Your Sideview Mirror Closer Than They Appear?

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Reasons Why Objects in Side View Mirror Seems Closer in San Diego, CA

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“Objects in mirror are closer than they appear.” This warning is emblazoned on every sideview mirror in the United States, and you likely don’t give it much thought. You’ve become used to adjusting your perception when using your sideview mirrors to watch for approaching traffic, knowing cars are closer than they seem. If you’ve ever wondered why this is the case, the answer is fairly basic: it’s about the shape of your sideview mirror. Altra Insurance, the expert car insurance San Diego is here to better explain this concept.

Sideview Mirrors Are Convex

Objects appear farther away than they really are in your sideview mirror because of their shape. Your mirrors are slightly convex, which means they curve on the sides and bow outward slightly in the middle. However, only your passenger-side mirror has this shape. The driver-side mirror is flat. 

Sideview mirrors are shaped this way to accommodate the angle of your view and eliminate blind spots. The driver-side mirror is flat because you’re viewing it from almost head-on and from a distance of about three feet. The passenger-side mirror is convex to eliminate blind spots and make it easy to see objects on the right side of your vehicle. You’re viewing your passenger-side mirror from about six feet away, so it needs to be curved to reflect a wide enough view of the right side of your car.

The Science of Perception

When you view images in your passenger-side mirror, they look smaller than they are in reality, and the objects seem farther away because your brain judges distance based on the relative size of different objects. How the light hits the surface of the mirror also plays a role. 

When light reflects off your flat driver-side mirror, it bounces off in the same direction, carrying the information to your eyes unaltered. The image your eyes produce will be accurate. Your driver-side mirror has a smaller focal point than your passenger-side mirror, and its viewing angle rapidly diminishes the further away you get, but this isn’t an issue when you’re sitting three feet from the mirror. 

When the light hits a curved mirror, the path the light takes to reach your eyes changes. As the light hits the center of your convex passenger-side mirror, it bounces straight to your eyes. As the light hits the edges of the curved mirror, it bounces farther before reaching your eyes, causing the light rays to converge. 

To your eyes, the image the light carries from a curved surface seems to be located where the rays converge. Because the light waves are diverging, they would actually converge if they continued to the other side of the mirror. The result is an image of the car in your passenger-side mirror that seems to be behind your mirror and at a greater distance. 

Images reflected in a curved mirror look smaller because they’re compressed. A curved mirror is used on your passenger side because it can reflect more information in a smaller space, giving you a wider field of view to see more to the right of your car with the safety trade-off of sacrificing accurate perception of distance.

Using your sideview mirrors is just one way to stay safe when on the road. Make sure you’re protected with adequate auto insurance in the event of an accident. At Altra Insurance Services, we don’t just provide top-quality car insurance. We also offer motorcycle, commercial, home, and renter insurance. San Diego residents can call 619-474-6666 today for a free quote.

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