Lift (force)

Lift is a special force that happens when a fluid moves around an object. A fluid is something that can flow, like the air around us or the water in an ocean.

When this fluid flows past a solid shape, it pushes on that shape. Lift is the part of that push that moves at a right angle to the flow. Most people think of lift as an upward force that fights against gravity.

However, lift can actually act in any direction as long as it stays perpendicular to the flow. If the fluid is air, we call it an aerodynamic force. If the fluid is a liquid, we call it a hydrodynamic force.

There are different ways that lift can work depending on the situation. One way is called aerostatic lift, or buoyancy. This happens when the fluid inside an object is lighter than the fluid outside.

This is how big balloons, blimps, and even submarines work without needing to move. Another way is called planing lift. This occurs when only the bottom part of an object sits in a moving liquid. You can see this happening with motorboats, surfboards, and even water-skis. These objects use the moving water to stay on top.

Scientists use different ideas to explain how wings create lift. One famous idea uses Newton's third law of motion. This law says that every action has an equal and opposite reaction.

As air flows over a wing, the wing pushes the air downward. Because the wing pushes the air down, the air must push the wing up with the same amount of force. This upward reaction is what we call lift. Another way to look at it is through Bernoulli's principle. Both of these ways are correct and help us understand the complex way fluids move.

It is hard to explain lift perfectly because the math is very complex. Many people try to use simple models, but these models often leave things out.

For example, some people wrongly claim that air travels faster on top because the path is longer. NASA experts have noted that many textbooks actually use incorrect diagrams or explanations. Even describing how the air turns around a wing is a very hard job. A change in velocity in one direction can cause a change in a perpendicular direction in a fluid. This is much more complicated than how solid objects move.

We see the power of lift in many parts of our world. It is not just for airplanes with fixed wings.

Many other things use streamlined shapes to create lift, such as propellers, kites, and helicopter rotors. Even racing cars use wings to create lift in a different direction. In nature, birds, bats, and insects all use lift to fly through the sky. Even some seeds from trees use it to travel through the air. It is a rule of nature that connects machines, animals, and plants.