Waldorf Matters … Fluid Mechanics

In our weekly blog series, Mr Murrell reflects on his Fluid Mechanics Main Lesson with Class 8

Class 8 are having a Main Lesson looking at both familiar and unexpected phenomena in fluids: liquids and gases . We investigated the  fact that  water in a container closed at the upper end, but open and submerged in water at the  bottom will be held in place. When the limits of this were investigated, atmospheric pressure was discovered . It happens that it is strong enough to hold up only a 32 foot column of water, just under ten meters.

Class 8 were  enthusiastic in putting  this to the test.

We put the  open end of the filled  hose pipe in the “well” at a low point  on the school site.

Next, we raised the  pipe up to the window level in the Eurythmy room.

A space appeared at the top of the hose because we were now 32 feet above the water in the well below. Atmospheric pressure could no longer hold up the water.

As we raised the tube higher the space expanded,  and then closed up again as we descended.

Historically these spaces were the first  man-made vacuums.

Close observation shows the water starts to boil even though it is still at room temperature. Its own weight pulling downwards has stretched it out to an incredibly low pressure.

Such an unusual barometer is rarely experienced and it was well worth it.

The whole idea of pressure gets enlivened in this way. Fifteen pounds per square inch  would be the weight of air in an imaginary hose pipe   stretching up through our whole atmosphere . It perfectly balances the  weight of a  32 foot column of water, or a 760 mm tube of the much denser mercury.

The pressure gradients  in the atmosphere and the oceans have nowadays been explored  thoroughly, but a simple local experiment like this one opens  the windows  to  these domains of nature in a new way.