======Magdeburg Hemispheres with Suction Cups======


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**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
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**Alternative titles:** Suction Cup Magdeburg Demo
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====Summary====                   
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====Procedure====  
  - Wipe the rubber faces of two glass-handling suction cups so they are clean and dry.
  - Press the cups together firmly and engage the vacuum levers to enlarge the sealed cavity and lower the internal pressure.
  - Have two students grasp one handle each and attempt to pull the cups straight apart while others observe the effort required.
  - If they separate easily, reseat the cups with greater care to ensure an airtight seal, then repeat.
  - Discuss how the outside air pushes inward on the exposed area and why a lower internal pressure increases the clamping force.



====Links==== 
Pulling Apart The Magdeburg Hemispheres - The Action Lab: 
{{youtube>x7Tbj2ee7t4?}}\\

Magdeburg Hemispheres- amazing alternate method- no pump - Homemade Science with Bruce Yeany: 
{{youtube>Q66DxZB6plE?}}\\

📄 Magdeburg hemispheres - Collection of Physics Experiments: [[http://physicsexperiments.eu/4304/magdeburg-hemispheres]]\\


====Variations====
  * See second video for a way to do this with no pump.
  * Contrast with a pair that has a small leak to show the role of sealing and damping.




====Safety Precautions====
  * Clear the area around the students in case the cups separate suddenly.
  * Instruct students to pull along the axis of the handles and not to twist, which can cause slips.
  * Keep fingers away from the meeting faces when engaging or releasing the vacuum levers.
  * Do not exceed the manufacturer’s rated load; inspect cups for damage before use.




====Questions to Consider====
  * What supplies the force holding the cups together? (The higher outside air pressure acting over the cup area.)
  * Why does increasing cup diameter make separation harder? (Greater area means a larger force for the same pressure difference.)
  * In Otto von Guericke’s original hemispheres, what created the pressure difference? (Air was pumped out of the enclosed volume, lowering the internal pressure.)
  * What would happen to the holding force at high altitude or inside a vacuum chamber? (Outside pressure is lower, so the holding force decreases.)
  * How could you estimate the pressure inside the sealed cavity from a measured pull? (Divide the measured separating force by the effective area to find the pressure difference, then subtract from atmospheric pressure to estimate the internal pressure.)