A Simple Water Tap Made Out of a Resealable Bottle and Two Straws
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Experienced outdoorsman Bora Cakir demonstrated a simple water tap that can be made using two straws and a bottle with a resealable cap. He explains that the straws, which are placed in a perpendicular manner, create air pressure that releases the water when the vertical straw is removed. The water is then stopped when the straw is replaced
It is possible to make a simple tap using air pressure. Note: Make sure that the holes where the straws will pass are not too big.
A commenter on the post explained the physics behind making this tap in more detail.
The straw creates an airtight seal with the red cap, and that airtight seal blocks off the air inside the bottle from the external atmosphere. The water can't flow out because that would mean that the air has to increase in volume, thereby decreasing in density and thereby pressure. In basic terms, the air in the bottle acts like a vacuum, sucking the water up to stop it from flowing out of the yellow straw.