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The water in a drinking straw does not drip out when you press te top of the straw with your thumb or finger tip?
Wiki User
∙ 14y ago
It's a matter of air pressure that acts on the water.
When the straw is uncovered, there are two forces acting on the water inside. There is gravity, pulling the water down, and air pressure. The pressure is about the same on both ends of the straw, but on the top of the straw, the pressure pushes the water downward, and on the bottom of the straw, the pressure pushes upward. Both of the pressures are the same, so the net force is just the force of gravity pulling the water down and out of the straw.
When you cover the top of the straw, you block the air from pushing down on the water. In this case, the only forces on the water are the air pressure pushing up, and gravity pulling down. However, the air pressure is a greater force than gravity, and keeps the water in the straw despite gravity's pull.
Wiki User
∙ 14y ago
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The water in a drinking straw does not drip out when you press the top of the straw with your thumb or finger tip?
there is no air
Why the water in a drinking straw does not drip out when you press the top of the straw with your thumb of finger tip?
Because under your thumb, inside the straw, there is now a vacuum which keeps the water in.
Why do the water in a drinking straw does not drip out when you press the top of the straw with your thumb or finger tip?
Because under your thumb, inside the straw, there is now a vacuum which keeps the water in.
Why does the drinking straw does not drip out when you press the top of the straw with your thumb or finger tip?
Your finger prevents air from entering through the top of the straw. As fluid moves down the straw it leaves a void in it's wake, one that is usually immediately filled by air. By preventing the air from entering the top of the straw, the fluid cannot move downwards because to do so would leave a vacuum space between your finger and the fluid; this "sucks" the fluid back in into place and prevents it from decending down the straw.
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