Bernoulli's principle facts for kids

A venturi showing Bernoulli's principle. The water on the right is lower due to the higher pressure in the big tube

Bernoulli's principle is a super important idea in fluid dynamics, which is the study of how liquids and gases move. It tells us that when a fluid (like water or air) speeds up, its pressure goes down. Think of it like this: if air is rushing really fast, it pushes less on things around it.

The picture on the right shows this happening with water in a special tube called a venturi. In the wider part of the tube, the water moves slower and has higher pressure. But when the water flows into the narrow part, it has to speed up to fit through. When it speeds up, its pressure drops. This drop in pressure is why the water level is lower on the right side of the tube.

When we talk about "pressure," we mean the force that a fluid pushes with over a certain area. Bernoulli noticed that when a fluid speeds up, its pressure decreases. This means that changes in a fluid's speed are always connected to changes in its pressure. This principle helps us understand many things, from how airplanes fly to how water flows through pipes.

What is Bernoulli's Principle?

Bernoulli's principle explains that the total energy in a moving fluid stays the same. This energy is made up of three parts:

• The fluid's pressure.
• Its kinetic energy (energy from its movement).
• Its potential energy (energy from its height).

So, if one part of the energy goes up, another part must go down to keep the total the same. For example, if the fluid speeds up (kinetic energy increases), its pressure must decrease. This idea works best for fluids that don't get thicker (no viscosity) and don't get squished (no compressibility).

How Does This Principle Work?

Imagine a fluid flowing through a pipe. If the pipe gets narrower, the fluid has to move faster to get the same amount of fluid through. When the fluid speeds up, it doesn't push as hard on the sides of the pipe. This means the pressure inside the pipe drops.

This is a bit like a busy hallway. If many people need to get through a narrow door, they have to speed up. As they rush through, they bump into the walls less often than if they were walking slowly in a wide-open space.

Real-World Examples

Bernoulli's principle helps us understand many things around us:

• Airplane Wings: Airplane wings are shaped so that air moves faster over the top surface than the bottom. This creates lower pressure above the wing and higher pressure below it, which lifts the plane into the sky.
• Carburetors: In older cars, carburetors used Bernoulli's principle to mix air and fuel. Air speeds up as it passes through a narrow part, causing a pressure drop that pulls fuel into the airflow.
• Sprayers: Many spray bottles and paint sprayers work by using a fast-moving stream of air or water to create low pressure, which then sucks up the liquid to be sprayed.

Images for kids

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  Condensation visible over the upper surface of an Airbus A340 wing caused by the fall in temperature accompanying the fall in pressure.