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Drag Force

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What is Drag?

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Drag Force Animation

Friction is the force that prevents rigid surfaces, fluid layers, and material elements from slipping against each other from moving in the same direction.

 

Several Types of Friction

  • The relative lateral motion of two solid surfaces in contact is resisted by dry friction.

  • The friction between layers of a viscous fluid that are moving relative to each other is referred to as fluid friction.

  • Lubricated friction occurs when two rigid surfaces are separated by a lubricant fluid.

  • Skin friction is a part of drag, which is the force that prevents a fluid from moving over a body's surface.

  • Internal friction is the force that opposes motion between the components that make up a solid material as it deforms.

 

What is Fluid Friction?

Fluid friction happens as two fluid layers move in opposite directions. Viscosity is the term for the internal resistance to flow. The viscosity of a fluid is often referred to as its "thickness."

All real fluids are viscous because they resist shearing in any way. The definition of an inviscid fluid, or an ideal fluid that gives no resistance to shearing and is therefore not viscous, can be useful.

 

Examples of Fluid Friction

  • If there is a wet surface between two thin glass plates, the plates will get trapped and the bottom plate will not break when only the top plate is held.

  • The extent of a splash when an object is dropped in a fluid is determined by the fluid friction of that fluid.

  • On the surface of moving water, lighter dust particles travel quickly. This is because the top layer of water has a high-velocity gradient due to lower dynamic fluid friction.

 

Drag Force Formula

The force that is exerted on a rigid body moving with respect to a fluid due to the fluid's movement is known as drag force. For instance, drag on a moving ship in the water or drag on a moving plane in the air. As a result, a drag force is the resistance force created by a body moving through a fluid such as water or air. This drag force is directed in the opposite direction as the oncoming flow velocity. As a result, the relative velocity between the body and the fluid is this.

 

Concept of Drag Force

A fluid's drag force is its resistance force. This force acts in the opposite direction of the motion of an object that is submerged in a fluid. As a result, drag force is described as the force that opposes a body's motion through a fluid.

Aerodynamic drag occurs when such motion of the body occurs in the fluid-like air. It's also a hydrodynamic drag if the fluid is water. Its natural tendency is to behave in the opposite direction of the velocity flow.

The maximum speed that a falling body can achieve is often limited by air resistance. The drag force, which is the force that objects experience when moving through a fluid, is exemplified here by air resistance.

Drag force, like kinetic friction, is reactive in that it only occurs while an object is moving and points in the opposite direction of the object's motion through the fluid.

This force is divided into two categories: shape drag and skin drag. The resistance of fluids to being moved out of the way by an object moving through the fluid causes form drag.

As a result, shape drag is close to the usual force given by solids' resistance to deformation. Skin drag is basically a mechanical frictional force induced by the fluid slipping over the moving object's surface.

Fluid density, Square of velocity, Drag coefficient, and Cross-section area all have an effect on its value.

 

What is Drag in Science?

Drag is the force that a fluid stream exerts on some object in its direction or that an object passing through a fluid feels. Designers of moving cars, ships, suspension bridges, cooling towers, and other structures must consider its size and how it can be minimized. Traditionally, drag forces are represented by a drag coefficient, which is determined regardless of the shape of the body. Dimensional analysis shows that the drag coefficient is proportional to the Reynolds number; the exact relationship must be determined experimentally, but it can be used to estimate the drag forces encountered by other bodies in other fluids at different speeds. When engineers use the effects of a model structure to predict the behavior of other structures, they use the concept of dynamic similarity.

FAQ (Frequently Asked Questions)

Q.1: A Vehicle Travels with a Speed of 80 km per h, with a Drag Coefficient of 0.25. If the Cross-Sectional Area is 6 square meters, then Find out the Drag Force.

Solution:

Velocity, V = 80 km per h = 80 x 5/18 m per sec 

= 22.22 m per sec

Drag Coefficient, 

CD = 0.25

Cross-sectional Area, A =6 square meter

Density of Fluid, 

Ρ = 1.2 kg per cubic m


The Drag Force Formula is:

D = 1/2 [ CD  × ρ × V2 × A]

​Substituting the values,

D = 1/2 [0.25  ×1.2 × 22.222 × 6 ]

D = 444.35 N

Therefore the drag force will be 444.35 N.

Q2 - What do You Mean by 'Streamlined Shape'? How does it Help in the Motion of Vehicles?

Ans - A streamlined form is one that flows in the same direction as a stream of water or air. Automobiles, cars, and airplanes have a special shape to minimize drag. Fluid pressure, either due to water in the case of ships or due to air in the case of vehicles, opposes the passage of automobiles, aircraft, and ships. Vehicles, helicopters, and ships are given a special form called the streamlined shape to minimize drag.

Q3 - Define Drag.

Ans - Drag is the force that a fluid stream exerts on some object in its direction or that an object passing through a fluid feels. Designers of moving cars, ships, suspension bridges, cooling towers, and other structures must consider its size and how it can be minimized. Traditionally, drag forces are represented by a drag coefficient, which is determined regardless of the shape of the body. Dimensional analysis shows that the drag coefficient is proportional to the Reynolds number; the exact relationship must be determined experimentally, but it can be used to estimate the drag forces encountered by other bodies in other fluids at different speeds. When engineers use the effects of a model structure to predict the behavior of other structures, they use the concept of dynamic similarity.