Drag (physics)

Air and water push on moving things.

This push is called drag. It works against the way an object moves. This means drag tries to slow things down.

Drag happens in different ways. One way is from the shape of an object. A wide shape catches more push. Another way is from rubbing. This is when the fluid rubs against a surface.

Drag also happens when things fly. Wings make lift to help planes stay up. This lift can also cause more drag.

Speed changes how drag works. Fast things feel a much bigger push. A runner uses energy to move through the air.

Everything that moves through air or water feels drag. It is a part of our world.

Drag is a force that pushes against moving objects.

This push happens when an object moves through a fluid. A fluid can be a liquid like water or a gas like air. Drag always works in the opposite direction of motion. This means it tries to slow things down.

There are different ways drag happens. Form drag comes from the shape of an object. A wide shape catches more fluid as it moves. Skin friction drag comes from rubbing. This happens when the fluid rubs against a surface.

For planes, these two types are called parasitic drag.

Wings also create a special type of drag. This is called lift-induced drag. It happens because wings must create lift to fly. As a plane flies faster, these types of drag change.

At low speeds, induced drag is large. At high speeds, parasitic drag grows. Pilots look for a speed where total drag is low. This helps the plane fly with great efficiency.

Drag is a force that pushes against objects moving through a fluid. A fluid is any substance that flows, like air or water. This force always acts in the opposite direction of motion. It works to slow things down as they move.

This push happens because the object must move the fluid out of its way. Drag is unique because it changes based on how fast an object moves. For low speeds, the force grows steadily with speed. At high speeds, the force grows much faster, specifically by the square of the velocity.

There are several ways this force works. Form drag comes from the shape of the object. It is caused by the pressure of the fluid as it flows around a body. Skin friction drag is caused by the fluid rubbing against a surface. This can happen on the outside of a boat or the inside of a pipe.

When you add these two together, it is called parasitic drag. This type of drag is always a negative thing for an aircraft. Other types, like lift-induced drag, happen because of how wings create lift.

Scientists use math to understand how these forces behave. They use a number called the Reynolds number to tell if flow is low-speed or high-speed. They also use a drag coefficient to describe how much a specific shape resists movement.

This coefficient depends on the shape and the Reynolds number. For a sphere, the coefficient changes as the speed changes. For other shapes, the coefficient might stay the same at high speeds. This helps engineers predict how much force an object will feel.

Engineers have used these facts to build better machines. For example, the Concorde was a famous supersonic aircraft. To reduce wave drag, which happens at very high speeds, engineers used the area rule. This rule helped reduce wave drag at Mach 2 by 1.8 percent. They did this by extending the rear part of the plane's body. This shows how changing a shape can change how it moves through the air. Even small changes in design can make a big difference in performance.

Understanding drag helps us see the world differently. It explains why a sprinter might use 5% of their energy just to fight the air. It also explains why cars and planes are shaped the way they are.

When an aircraft flies, pilots look for a special speed. At this speed, the total drag is at its lowest point. This allows the plane to fly with the best efficiency. Knowing these patterns helps us move through our world more easily.

Drag, also known as fluid resistance or viscous force, is a force that acts opposite to the direction of motion for any object moving through a fluid. In physics, a fluid is any substance that flows, such as air or water. This force works to decrease the velocity of the fluid relative to the solid object in its path. Unlike many other resistive forces, drag is uniquely dependent on velocity. This means the faster an object moves, the more the force changes.

To understand how drag works, we must look at the relationship between speed and resistance. This relationship is often measured by the Reynolds number, which distinguishes between low-speed and high-speed flow. In low-speed flow, the drag force is proportional to the relative velocity. However, in high-speed flow, the drag force becomes proportional to the velocity squared. This shift has a massive impact on the power required to move. For example, the power needed to overcome drag increases as the cube of the velocity.

There are several distinct types of drag caused by different physical interactions. Two primary types apply to all objects: form drag and skin friction drag. Form drag, or pressure drag, is caused by the pressure exerted on an object as fluid flows around it. This is determined by the object's cross-sectional area and shape. Skin friction drag, also called viscous drag, is caused by friction between the fluid and the object's surface. This can occur on the outside of a boat hull or the inside of a pipe.

In the field of aeronautics, these forces are often categorized as parasitic drag. Parasitic drag is the sum of form drag and skin friction drag. It is considered entirely negative for an aircraft. Another important type is lift-induced drag, which occurs when a three-dimensional body, like a wing, creates lift. This includes vortex drag from trailing vortices and additional viscous drag. As a wing's angle of attack increases, the lift coefficient increases, and so does the lift-induced drag.

At very high speeds, aircraft encounter wave drag. This occurs when local flow velocities become supersonic, creating shockwaves. Engineers have used specific design rules to manage this. For the supersonic Concorde prototype, engineers applied the area rule to reduce wave drag at Mach 2. By extending the rear fuselage on the production aircraft, they reduced wave drag by 1.8%.

Scientists use the drag equation to calculate the force acting on an object. The equation includes the density of the fluid, the velocity of the object, the cross-sectional area, and the drag coefficient. The drag coefficient, or Cd, is a dimensionless number that depends on the object's shape and the Reynolds number. For a streamlined body, like an airfoil, drag is dominated by viscous forces. For a bluff body, like a road vehicle, drag is dominated by pressure forces.

Understanding these proportions helps engineers design efficient machines. For aircraft, the total drag curve shows a minimum at a specific airspeed. Flying at this speed allows for optimal efficiency, helping pilots maximize endurance or gliding range. Even in human athletics, drag is a major factor. A top sprinter may use 5% of their total energy output just to overcome drag.