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The Physics Behind An Airplane Propeller


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    One of the things I'd like to share today is something I had wondered for most of my childhood. My dad is an aeronautical engineer, and other members of my family have spent a lot of time around airplanes as well. One thing I had always wondered growing up was when you look at an airplane's propeller from the front, especially when it starts up. It almost looks like it's going in reverse. The same can be said for car wheels. So I asked my dad why this happens. Here's something that I found that will put it scientifically about what is called the backward motion illusion:

    The backward motion illusion occurs when the speed of rotation is such that--in the interval between each frame--a new blade moves nearly into the position occupied by a blade in the previous frame. If the timing is precise, it looks like the propeller did not turn at all.

    This video does a good job of showing how are brain processes the information. Pretty cool huh?

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    Happy Trippy. Good video, thanks for the share. That is really cool. I assumed it was something like this but never knew the exact explanation. Makes me think of all the times I have played around with this by staring at my ceiling fan, trying to follow just one blade's rotation.
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    Cosmic Kid Wrote: Happy Trippy. Good video, thanks for the share. That is really cool. I assumed it was something like this but never knew the exact explanation. Makes me think of all the times I have played around with this by staring at my ceiling fan, trying to follow just one blade's rotation.
    Very true. I used to think it had to be something wrong with my eyes. Wink When you look at some propellers, their blades tend to bend with resistance, which adds to the trippiness in my opinion.