Why do some car side mirrors make objects look smaller and farther away?
The short answer
Some car side mirrors use a mirror that curves outward, called a convex mirror. It shows a wider area than a flat mirror, but vehicles appear smaller in it. Because of that, they can seem farther away than they really are.
How a convex mirror shows a wider area
When light hits a mirror and bounces off, we call it reflection. A flat mirror follows the same reflection rule everywhere on its surface. A convex mirror curves outward, so different parts of it face slightly different directions. As a result, it sends reflected light in more directions and shows a wider area.
Why the image looks smaller
Light reflected from a convex mirror spreads out. When it reaches your eyes, it seems to have come from a place behind the mirror. You see an image there, even though no object is actually behind the mirror. This image is smaller than the real object and stays right way up. It is called a virtual image.
In everyday life, a car that is farther away usually looks smaller. A convex mirror also makes the image smaller, so a vehicle in it can seem farther away than it really is. The U.S. National Highway Traffic Safety Administration also explains that convex mirrors show a wider area behind a vehicle, but can make objects seem farther away.
Not all side mirrors are the same
Car side mirrors can be flat or convex. Their shape and view vary by vehicle, so distance can look different from one mirror to another. The owner’s manual can explain the mirrors fitted to a particular car.
Key point
- A convex mirror shows a wider area than a flat mirror.
- Objects in it look smaller and can seem farther away than they are.
- The shape and view of a side mirror vary from car to car.