2B30.30-Magdeburg Hemispheres

Video: Watch this demo

Instructor’s video

Description: This demonstration shows the force of atmospheric pressure.
Attach the hemispheres and use a vacuum pump to remove the air inside. Now have a student try and open it.

Equipment:

• Vacuum pump
• Magdeburg Hemispheres

Setup Procedure:

1. Plug the vacuum pump in and make sure it works.

Demonstration Procedure:

1. Have a small student pull apart the hemispheres with the vacuum pump off (easy).
2. Now, turn on the vacuum pump and have a strong student try and pull them apart (very hard).
3. Explain that since there is basically a vacuum inside the hemispheres, the atmospheric pressure is keeping them together.
4. Explain that to open these, the student would have to pull with a force of about 250 pounds.
5. (Optional) To do this out, say the radius of each disk is 1.6in. The surface area (pi*r*r) is thus about 16 square inches for both spheres. The atmosphere has on about 14.7 PSI, so that comes out to about 280 pounds of force.
6. When finished, turn off the vacuum pump.

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