# U-tube: Water Rises Slightly - Get Help on the Right Track

• hansel13
In summary, a U-tube is a simple device used in science experiments to demonstrate fluid displacement and buoyancy. It consists of a U-shaped tube filled with water or another liquid. The liquid in the two arms of the tube will be at the same level when the tube is horizontal, but when one arm is raised, the liquid in that arm will rise while the liquid in the other arm will fall due to the pressure difference caused by the change in height. This is due to the principle of buoyancy, which causes the water to rise slightly in one arm of the U-tube. U-tubes can be used in science experiments to demonstrate various principles of fluid mechanics and can even be used to measure the volume of a gas by filling
hansel13

## Homework Statement

A person blows across the top of one arm of a U-tube partially filled with water. The water in that arm...?
The answer is rises slightly: The water in that arm rises slightly.

I really couldn't figure out why. Could someone help get me on the right track?

What do you know about air pressure, and how does that pressure depend on the velocity of the air?

I can offer an explanation for why the water in one arm of the U-tube rises slightly when air is blown across the top. This phenomenon is due to the principle of fluid dynamics, specifically Bernoulli's principle. When air is blown across the top of the U-tube, it creates an area of low pressure above the water level in that arm. This low pressure causes the water to rise slightly in order to equalize the pressure on both sides of the tube. This is similar to how a straw works when you suck on it - the low pressure in your mouth causes the liquid in the straw to rise up to equalize the pressure. Additionally, the shape of the U-tube allows for this movement of water due to its curved shape and the surface tension of the water. I hope this explanation helps you better understand the concept.

## 1. What is a U-tube?

A U-tube is a simple device used in science experiments to demonstrate the principles of fluid displacement and buoyancy. It consists of a U-shaped tube filled with water or another liquid.

## 2. How does a U-tube work?

In a U-tube, the liquid in the two arms of the tube will be at the same level when the tube is horizontal. When one arm is raised, the liquid in that arm will rise while the liquid in the other arm will fall. This is due to the pressure difference caused by the change in height of the liquid.

## 3. Why does the water rise slightly in one arm of the U-tube?

The water rises slightly in one arm of the U-tube because of the principle of buoyancy. When an object is submerged in a fluid, it experiences an upward force equal to the weight of the fluid it displaces. In this case, the water in the raised arm of the U-tube is displacing more water in the other arm, causing it to rise slightly.

## 4. How is a U-tube used in science experiments?

A U-tube can be used to demonstrate various principles of fluid mechanics, such as the relationship between pressure and depth in a fluid. It can also be used to measure the density of liquids or to compare the buoyancy of different objects.

## 5. Can a U-tube be used to measure the volume of a gas?

Yes, a U-tube can be used to measure the volume of a gas by filling one arm of the tube with the gas and the other with a liquid, such as water. The volume of the gas can be determined by measuring the difference in height of the liquid in the two arms.

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