# The Naked Scientists Forum

### Author Topic: Why do objects in the rear view mirror appear closer than they are?  (Read 10502 times)

#### chris

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##### Why do objects in the rear view mirror appear closer than they are?
« on: 17/02/2012 09:11:40 »
Is this an intentional aspect of mirror design? Why does it happen?

#### Geezer

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• "Vive la résistance!"
##### Re: Why do objects in the rear view mirror appear closer than they are?
« Reply #1 on: 17/02/2012 10:02:19 »
errrr, I think you got it downside up.

The text on the mirror should say "Objects in mirror are closer than they appear"

It's because the (usually) nearside mirror is convex to increase its field of view. The idea is to make sure you are aware of any vehicles that might be sneaking up on your "inside" before you move back into the "slow lane".

#### imatfaal

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##### Re: Why do objects in the rear view mirror appear closer than they are?
« Reply #2 on: 17/02/2012 10:32:07 »
The Geezer is right.  I offer this incontrovertible proof - well actually it's just a movie still

I still cannot embed pictures in the post without the workaround

#### Phractality

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##### Re: Why do objects in the rear view mirror appear closer than they are?
« Reply #3 on: 17/02/2012 19:23:07 »
The image you see in a convex mirror is called a virutal image. The virtual image, which is located behind the mirror from your perspective, is closer than the actual object, so our eyes converge to a point which is closer than the object. If we could judge distance by convergence of your eyes, you'd think the object is closer than it actually is. However, the angular size of the virtual image is smaller than the angular size of the object. We tend to estimate distance by angular size rather than by the angle of convergence of our eyes, so the think the object is farther than it really is.
Image source.

#### SeanB

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##### Re: Why do objects in the rear view mirror appear closer than they are?
« Reply #4 on: 17/02/2012 19:29:53 »
This as well....

#### The Naked Scientists Forum

##### Re: Why do objects in the rear view mirror appear closer than they are?
« Reply #4 on: 17/02/2012 19:29:53 »