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Fan Blades: Newsletter Challenge (10/04/05)

Posted October 04, 2005 7:00 AM

The question as it appears in the 10/03 edition of Specs & Techs from GlobalSpec:

It was an especially hot day in late August and Joe has been out mowing his lawn. He comes in, takes a shower and lies on the bed under the ceiling fan for a few minutes to cool off. As he watches the blades spin around, he tries to remember if the fan had 3, 4 or 5 blades. He tries to count the blades by following them with his eyes, but the bright light bulbs suspended below it hurt his eyes and he keeps losing his place as his eyes try to jump from one blade to the next. He thinks about the problem for a minute, then figures out a way to count the blades without hurting his eyeballs. How does he do it?

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The Engineer
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#1

Not Sure

10/04/2005 9:04 AM

He could try counting the shadows from the blades on the floor, I'm not sure if they would be distinct enough, though it did say "bright lighbulbs"

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#2
In reply to #1

Re:Not Sure

10/04/2005 6:19 PM

That would put the shadows on the ceiling not on the floor. I imagine turning the fan off or asking the wife if she knows isn't going to be it either.

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The Engineer
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#10
In reply to #2

Re:Not Sure

10/06/2005 8:59 AM

You're right, missed the "suspended below" part.

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Associate

Join Date: Sep 2005
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#3

Fan Blades

10/04/2005 11:19 PM

That is sample. Just switch "on" another table fan for cooling. Then switch "off" the ceiling fan and you can count the fan blade. Isn't that simple. If you want to count the fan blades with the fan running, wear Rayban sun glass so that the bright light from the bulb is shield off.

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Participant

Join Date: Oct 2005
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#4

simple stuff...

10/05/2005 1:01 AM

get a camera...hi def...and tk a pic. simple or digital camera would work as well... TOO simple!

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Active Contributor

Join Date: Oct 2005
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#5
In reply to #4

Re:simple stuff...

10/05/2005 1:42 AM

Blink your eyes really fast. It'll be like watching an olde tyme flick.

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Guru
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#6

Not so simple solution

10/05/2005 7:52 AM

Assuming simply switching the fan off is not the answer, how about switching the bright lights on and off at the right frequency to "lock" the blades - the old strobe effect where the rotating m/c appears stationary.

Ceiling fans usually turn slow enough to make this possible - maybe!

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Active Contributor

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#7
In reply to #6

Re:Not so simple solution

10/05/2005 8:53 AM

I'm not sure, but I'm going to have to go home and try it. Somebody wake me in about two hours...

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#8

Ceiling Fan

10/05/2005 9:28 AM

If the blades are casting shadows on the ceiling, he could check the angle between the shadows. If it is a right angle, then 4 blades; greater than a right angle, 3 blades; and finally if less than a right angle, 5 blades. If the room he is in is rectangular (likely for a home), then it would be easy to judge if the angles formed by the blades' shadows are right or not.

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Guru
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#9
In reply to #8

Re:Ceiling Fan

10/06/2005 7:41 AM

I like this one - it's got a "why didn't I think of that" feel about it!

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Participant

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#11
In reply to #9

Re:Ceiling Fan

10/10/2005 2:03 AM

That should read... "Why did I think of that?" If you cant see the angle of the blades because of their speed, how can you hope to see their shadows?

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#12

And the Answer is...

10/11/2005 3:00 PM

As written in the 10/11 issue of Specs & Techs from GlobalSpec:

He closes his eyes, waits a little while, then rapidly opens and re-closes his eyes. The bright illumination from the incandescent lamps helps form an after-image in his eyes, clearly showing five fans blades frozen in an instant of time. The process is like pulsing a strobe light, only now the incandescent lamps provide steady illumination and he uses his eye lids as a shutter to capture an instant of the motion.

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Guru
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#13
In reply to #12

Re:And the Answer is...

10/18/2005 10:22 AM

Doh! How many times have I done just this to look at something rotating or flashing? I may be drummed out of DRC (Dogbert's Ruling Class)for this!!

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Member

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#14

Use your head

10/31/2005 8:18 AM

Stand up on the bed, count the times the fan blades hit your head during one revolution.

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