Untitled Document

Physics Demo Number: 146

Approximate

Run Time: 10 min

Magdeburg Hemispheres and Pressure

Demo Description

Put the two hemispheres together.

Be sure that their 'o-ring seal' is clean and functioning.

Pump the air out of the sphere.

Try to separate the two halves by pulling on their handles.

Scientific Principles

Atmospheric pressure exerts a large force on surfaces that have vacuum on the other side.

Equipment

Vacuum Pump
Hemispheres

Equipment Location

Right rear wall shelf [H-4-3] of the storeroom houses the vacuum pump.
Kit (146) housed on Right Rear Wall shelf [H-4-2] contains the hmispheres

Instructions

The photo shows two sets of o-ring- hemispheres, an old brass totally pump- free Magdeburg device and the new vacuum pump resting on a cart. The equipment now stays on the dedicated shelves mentioned above :[H-4-3] and [H-4-2].

The pump in the previous picture is seen in more detail in the following picture.

Safety Note:

If one chooses to have two students pulling on the two handles, one needs to have two to three more students standing behind each of the two pullers, prepared to stop the pullers as they come lunging backwards in the event of an unwanted successful separation of the hemispheres.

It is always prudent to plan on safety backups when exerting large forces whose equilibrant forces can suddenly (and unexpectedly) disappear.