Matter & Energy · Depth 5 · Intermediate · 2 min read
Drag
Drag is the air resistance that pushes back on anything moving through air. Its strength depends on shape, surface, speed and the air itself.
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What is drag?
Drag is the aerodynamic force that opposes an object’s motion through the air.[1] Like lift, it is a mechanical force: it needs a fluid in contact with the object, and motion between the two.[1] On an airplane, the job of the engines is to overcome drag.[3]
What makes drag bigger or smaller
Drag depends on the object’s speed relative to the air, on how smooth or rough its surface is, on properties of the air such as its viscosity, and on the object’s shape.[1]
Shape has a very large effect. In one comparison, a flat plate facing the flow has a drag coefficient of about 1.28, while a streamlined airfoil shape has about 0.045, nearly thirty times less.[2] Changing the downstream (rear) shape of an object is one way to reduce its drag.[2]
The drag equation (optional)
Engineers estimate drag with a formula that mirrors the lift equation:[4]
D = CD × ½ ρ V2 × A
- D is the drag force.
- ρ is the air density.
- V is the speed.
- A is a reference area. Depending on the object, this can be its total surface area, its frontal area or its wing area.
- CD, the drag coefficient, captures the effects of shape, tilt, viscosity and compressibility.[4]
The key lesson is the V2: drag grows with the square of speed, so doubling your speed multiplies drag by four.[4] Drag coefficients are almost always measured in wind tunnels rather than calculated.[4]
Kinds of drag
NASA’s guide names several sources of drag:[1]
- Skin friction: air rubbing along the surface.
- Form drag: caused by the object’s shape and the pressure around it.
- Induced drag: “drag due to lift”, linked to the swirling vortices at the wing tips.
- Wave drag: from shock waves that form as an aircraft approaches the speed of sound.
- Ram drag: from slowing down the air that enters engines and cooling inlets.
Real-life examples
Winglets on airliners
Many modern airliners have upturned winglets at the tips of their wings. Their job is to reduce drag.[5]
Streamlining a model rocket
Adding a small cone-shaped fairing to the back of a model rocket reduces its drag compared with a blunt, blocky end.[2]
Why speed costs so much
Because drag depends on speed squared, going from 50 to 100 km/h doesn't double the air resistance: it quadruples it.[4]
Approaching the speed of sound
As an aircraft approaches the speed of sound, shock waves form and add a new kind of drag: wave drag.[1]
Connected across the map
- AircraftHow an airplane's parts work together: wings for lift, engines for thrust, and hinged surfaces that let the pilot steer in three directions.
- FrictionThe force that resists surfaces sliding over each other. Why it exists, why starting is harder than keeping going, and how we use it or fight it.
- ForcesA force is a push or a pull with a size and a direction. Forces start, stop and steer every motion, including an airplane's flight.3 branches
Learn more
Short descriptions are our own summaries. The resources belong to, and are run by, their publishers.
- Elementary Airfoil Interactive ↗
by NASA
Change a wing’s shape, angle and speed and watch how much lift and drag it makes.
- Beginner’s Guide to Aeronautics ↗
by NASA
NASA Glenn’s free, illustrated guide to how airplanes and rockets fly, from the four forces to engines and wind tunnels.
Evidence & sources
Supported by extensive evidence and broad scientific consensus.
Why this level? Drag, its main types and the drag equation are well-established aerodynamics, described here from NASA's Glenn Research Center.
This is a Knowledge Atlas editorial classification of the sources we could find, not a certificate of truth. How we evaluate knowledge
Sources
Based on 5 sources from 1 institution: NASA.
Show all 5 sourcesHide the list
- National Aeronautics and Space Administration· Government agencyWhat is Drag?Opened and checked against this page on 28 Sept 2026
- National Aeronautics and Space Administration· Government agencyShape Effects on DragOpened and checked against this page on 28 Sept 2026
- National Aeronautics and Space Administration· Government agencyFour Forces on an AirplaneOpened and checked against this page on 28 Sept 2026
- National Aeronautics and Space Administration· Government agencyThe Drag EquationOpened and checked against this page on 28 Sept 2026
- National Aeronautics and Space Administration· Government agencyAirplane Parts and FunctionOpened and checked against this page on 28 Sept 2026