Two suction cups are pressed together to create a low-pressure cavity between them. The higher outside air pressure pushes the cups together so strongly that students find it difficult to pull them apart, illustrating how pressure differences create large forces.

1. Wipe the rubber faces of two glass-handling suction cups so they are clean and dry.
2. Press the cups together firmly and engage the vacuum levers to enlarge the sealed cavity and lower the internal pressure.
3. Have two students grasp one handle each and attempt to pull the cups straight apart while others observe the effort required.
4. If they separate easily, reseat the cups with greater care to ensure an airtight seal, then repeat.
5. Discuss how the outside air pushes inward on the exposed area and why a lower internal pressure increases the clamping force.

Pulling Apart The Magdeburg Hemispheres - The Action Lab:

Magdeburg Hemispheres- amazing alternate method- no pump - Homemade Science with Bruce Yeany:

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

• 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.

• 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.

• 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.)