Why does water stay in the straw with your thumb over it?

Sealing the top of a straw with your finger stops air entering and exerting a downward force on the liquid, leaving only the upwards force of air pressure from below. These two effects cancel each other out leaving gravity as the dominant force causing the suspended liquid to drop out the bottom.

Why doesn’t liquid fall out of a straw if your thumb is covering the top opening as you lift it up out of a beverage?

It is because of pressure. When you suck from one end of the straw you create a low pressure (lower than atmosphere) inside the straw. The fluid outside the straw is comparatively at high pressure (atmospheric pressure) and thus it starts pushing the fluid inside the straw upwards. It is because of pressure.

How does water stay in a straw when you hold the top?

When you hold a finger over the straw, the column of liquid has a vacuum at one end (under your finger) and atmospheric pressure pushing up at the other end. The straw can hold the liquid as long as the pressure from the column of liquid is less than the pressure on the bottom from the atmosphere.

What force holds water in a straw?

Capillary forces are due to the liquid being attracted to the walls of the straw. Since the straw has a lot of surface area exposed to the liquid inside, these capillary forces are important and contribute to holding the liquid inside.

Why does water not fall out of a straw when it is closed on one end?

This is because the atmosphere exerted a pressure upwards from the bottom to prevent the water from falling (the headspace above the water has some small downwards pressure that is minimized by the incompressibility of water). The net force is zero, so the water doesn’t move.

How do you close one end of a straw?

Tear the wrapping off half of the straw, so that one end is exposed. Put the exposed end in your mouth, take aim, and blow! The wrapper shoots off the other end, like a dart from a blowgun. (Do not do this at close range, and do not aim at anyone’s face, please.)

How is straw made?

Straw is an agricultural byproduct consisting of the dry stalks of cereal plants after the grain and chaff have been removed. It makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat.

Can you drink through a straw on the moon?

It can’t, because there is no such force as “suction,” only atmospheric pressure rushing in to fill the void. On the moon (outside a pressurized habitat) there is no air pressure, so straws don’t work.

What happens when you place a straw in a drink?

The liquid rises in the straw, to exactly the same height as the liquid in the glass. That’s because the atmosphere is pushing down on the liquid in the glass. Now the atmosphere is pushing down on the liquid in the glass, with noting the balance it inside the straw, so the liquid rises…into your mouth!

How does sealing the top of a straw with your finger?

Sealing the top of a straw with your finger stops air entering and exerting a downward force on the liquid, leaving only the upwards force of air pressure from below. This upwards force is stronger than the force of gravity pulling down on the liquid.

How much force does air exert on a straw?

Molecules of air in the atmosphere push on everything and the force exerted by this is roughly one kilogram per square centimetre. Sealing the top of a straw with your finger stops air entering and exerting a downward force on the liquid, leaving only the upwards force of air pressure from below.

How do you get a liquid out of a straw?

Take your finger away from the straw and the downward force of the air pressure on the liquid will be the same as the upward force. These two effects cancel each other out leaving gravity as the dominant force causing the suspended liquid to drop out the bottom. Answered by Rik Sargent.

Why does a glass of wine fall out of a straw?

This upwards force is stronger than the force of gravity pulling down on the liquid. Take your finger away from the straw and the downward force of the air pressure on the liquid will be the same as the upward force. These two effects cancel each other out leaving gravity as the dominant force causing the suspended liquid to drop out the bottom.