Core Concept
Definition of principle: Bernoulli’s Principle explains what happens to pressure when a fluid like air or water speeds up or slows down. When the fluid moves faster, its pressure becomes lower. When the fluid moves slower, its pressure becomes higher. This means pressure and speed are linked in opposite ways.
Inverse relationship: The principle shows a special kind of relationship called an “inverse relationship.” That means when one thing goes up, the other goes down. So, when the speed of the fluid goes up, the pressure goes down, and when the speed goes down, the pressure goes up.
Relationship of Fluid Speed and Pressure
Streamline flow behavior: In streamline flow (which means smooth, steady movement of the fluid), the parts of the fluid that are moving faster always have lower pressure. This happens because energy is being used more for movement than for pressing outward.
Slower flow behavior: In areas where the fluid is moving more slowly, it has more time to press against things around it. This creates higher pressure in those slower parts of the flow.
Common phenomenon: You can see this speed-pressure connection in many real-life examples. Whether it’s air flying over airplane wings or water moving through a pipe, Bernoulli’s Principle helps explain how the fluid behaves.
Applications of Bernoulli’s Principle
Aerofoils in Aircraft
Aerofoil shape effect: The wings of an airplane are not flat all over. The top of the wing is curved while the bottom is flatter. This special shape helps make the air move differently above and below the wing.
Faster upper airflow: Because of the wing’s shape, air moves faster over the curved top. When the air goes faster, its pressure becomes lower.
Slower lower airflow: Under the wing, the air moves slower. Slower air means higher pressure. So now there’s more pressure pushing up from the bottom than from the top.
Lift generation: This difference in pressure creates a lift force. The lift pushes the airplane upwards, helping it take off and stay in the air.
Bunsen Burners
Gas velocity effect: In a Bunsen burner, gas comes out quickly through a small hole or nozzle. Because it’s moving fast, the pressure in that area drops.
Air intake by pressure difference: Since the pressure of the fast gas is lower, the surrounding air (which has higher pressure) gets pushed into the burner. This is how air gets pulled into the gas flow.
Air-fuel mixing: The air that gets pulled in mixes with the gas inside the burner. This mixture then burns at the top of the burner to create a strong, steady flame.
Car Spoilers and Wings
Inverted aerofoil design: Car spoilers are shaped like airplane wings that are flipped upside down. This upside-down design isn’t an accident—it’s done on purpose to create an effect opposite to lift. Instead of making the car rise, the shape uses Bernoulli’s Principle in reverse to push the car downward and help it stay on the road.
Airflow pattern: As the car moves forward, air flows around the spoiler. The air under the spoiler moves faster than the air above it. According to Bernoulli’s Principle, faster-moving air has lower pressure. So, the bottom of the spoiler has lower pressure, and the top has higher pressure.
Stability from downforce: This pressure difference causes a downward force on the car, called downforce. Downforce helps the car stay pressed to the road, especially when it is moving very fast. This makes the car easier to control and gives it better grip on the road so it doesn’t slide or lose balance.
Venturi Effect
Flow through constriction: When a fluid like air or water flows through a narrow part of a tube or pipe, it has to speed up to keep the flow going. This change in speed happens naturally so that the same amount of fluid keeps moving without any gaps.
Pressure reduction: As the fluid speeds up in the narrow section, the pressure in that area goes down. This is a perfect example of Bernoulli’s Principle, which shows that when speed increases, pressure decreases.
Demonstration of principle: The Venturi effect is one of the simplest ways to prove Bernoulli’s Principle. You just need a pipe that narrows in the middle and some flowing liquid or air to see the effect in action.
Movement of Ping Pong Balls
Spin and airflow interaction: When a ping pong ball spins as it moves through the air, the spinning changes how air flows on each side of the ball. On one side, the spin makes air flow faster. On the other side, the air moves slower.
Pressure imbalance: Faster air means lower pressure, and slower air means higher pressure. Because of this difference, the ball gets pushed toward the side with lower pressure.
Curved motion: This push makes the ball curve or swerve in the air instead of flying in a straight line. That’s why in table tennis, spinning the ball can make it curve and trick the other player.
Spray Guns
Air jet creates suction: A spray gun uses a jet of fast-moving air that flows across the top of a tube filled with liquid. The speed of the air causes the pressure above the liquid to drop.
Liquid rise by pressure difference: Because the pressure above the liquid is now low and the pressure below is higher, the liquid is pushed upward into the stream of fast air.
Atomization: When the liquid reaches the fast-moving air, it gets broken into very small drops. This process is called atomization. It creates a light mist or spray, which is perfect for painting surfaces or applying cleaning chemicals.
Air Flow over Curved Surfaces
Curved surface behavior: When air flows over a curved surface, such as a wing or a spinning ball, the air speeds up over the curve. Faster air means lower pressure, so the pressure drops over the curved part.
Broader application: This pressure change explains how airplanes lift off the ground and how race cars stick to the road at high speeds. Both flying and driving use curved shapes to guide air in ways that control pressure and improve performance.
Summary
Principle significance: Bernoulli’s Principle teaches us how the speed of a moving fluid, like air or water, affects its pressure. When the fluid moves faster, the pressure becomes lower. When the fluid moves slower, the pressure becomes higher. This simple rule helps explain many real-life things.
Engineering and natural relevance: Bernoulli’s Principle is useful in many areas of engineering and nature. It helps us understand how airplanes fly, how race cars stay steady, how spray bottles work, and even how balls curve in sports. Scientists and engineers use this idea when they design machines or products that need to control the flow of air or liquid.