======Strobe Light Fan======


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**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
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**Categories:** {{$demo.categories}}
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**Alternative titles:** Freezing a Spinning Fan
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====Summary====                   
{{$demo.summary}}



====Procedure====  
  - Place a desk fan or ceiling fan in a dimly lit room.  
  - Turn on the fan at a steady speed.  
  - Shine a strobe light directly at the fan blades.  
  - Adjust the strobe frequency:  
    - When the strobe rate matches the rotation speed, the blades appear frozen in place.  
    - When the strobe rate is slightly faster, the blades appear to move slowly forward.  
    - When the strobe rate is slightly slower, the blades appear to move slowly backward.  
  - Try different fan speeds to observe changes in apparent motion.



====Links==== 
Spinning Fan with Strobe Light - PHYSICS EVERYWHERE !: 
{{youtube>FlZ4BU_9NA8?}}\\

Motion - Strobe Light and Fan Demo Explained (READ WARNING BELOW!) - Jon White: 
{{youtube>83XPg9K8FI8?}}\\

📄 Measuring the Speed of Moving Objects with Stroboscopic Photography - Science Buddies: [[https://www.sciencebuddies.org/science-fair-projects/project-ideas/Photo_p003/photography-video/measuring-the-speed-of-moving-objects-with-stroboscopic-photography]]\\

====Variations====
  * Place a piece of tape or mark on one blade tip to make the effect easier to observe.  
  * Try with fans of different sizes (small desk fan vs large ceiling fan).  
  * Record the effect with a phone camera for comparison with real slow-motion video.




====Safety Precautions====
  * Do not put hands near moving fan blades.  
  * Avoid prolonged exposure to the strobe light as it may trigger discomfort or seizures in sensitive individuals.  
  * Keep the strobe light at a safe distance from the fan.




====Questions to Consider====
  * Why does the fan appear frozen when the strobe matches the blade speed? (Because each flash shows the blades in the same position, creating the illusion of stillness.)  
  * Why can the fan appear to spin backward? (If the strobe flashes slightly slower than the rotation speed, each flash shows the blades a little ahead, giving the illusion of reverse motion.)  
  * How is this similar to the “wagon wheel effect” in old movies? (Both are caused by stroboscopic sampling of motion at discrete time intervals.)  
  * What real-world uses are there for strobe lights besides demonstrations? (Studying vibrations, measuring machine speeds, and in entertainment lighting.)