# Torricelli's experiment

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Equipment: water, brown food color, 12 meters long PVC hose (diameter 8 mm), plastic can, cord, pulley in a tripod, scissors, small vice.

How to prepare: boil two liters of water (to remove the air dissolved in water), color the cooled water by a food color.
Place the tripod with a pulley somewhere where is at least 11 meters high place (stairway, wall, ...) , put a cord in a pulley so that both edges of the cord touch the ground.
Make tho holes in the top of a can so that the hose fits in it.

How to make: pour the colored water inside the can, close it by the top and drag the hose through one hole so that it touch the bottom. You can use a pot too but make sure that the edge of the hose cannot leave the bottom.
Fill all the hose by the water and close the edge by the vice. Fasten the cord to the vice.
Pull the other edge of the cord - the hose goes up. The water stil filles all the hose. The breakpoint is in the height of 10 meters - the hose goes up but the water stays at this point. Over the water there is a vacuum - you can show it when you lower the hose back - there is no bubble.

How to explain: Water follows the hose thanks to the pressure of the air - the pressure force pointing to the surface of the water in the can. The 10 meters high column of the water makes the same pressure as the air - there is no reason for water to goes up anymore.

How to use: use this experiment while teaching about the pressure of the air - you can also count the pressure.

Notes: Mr. Torricelli used mercury for this experiment but we cannot use it in czech schools. If you have more hoses, use different liquids - there will be columns of different heights thanks to different densities.

 Can and hose Closed edge of the hose Connecting of hose and can Overall view (hose iscolored for better view) Upper pulley Upper tripod Higher column of vaccum Lower column of vacuum
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