Drag (physics)

In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) refers to forces acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers (or surfaces) or a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, drag forces depend on velocity. Drag force is proportional to the velocity for a laminar flow and the squared velocity for a turbulent flow. Even though the ultimate cause of a drag is viscous friction, the turbulent drag is independent of viscosity.

Drag forces always decrease fluid velocity relative to the solid object in the fluid's path.

Examples of drag

Examples of drag include the component of the net aerodynamic or hydrodynamic force acting opposite to the direction of movement of the solid object relative to Earth as for cars, aircraft and boat hulls; or acting in the same geographical direction of motion as the solid, as for sails attached to a down wind sail boat, or in intermediate directions on a sail depending on points of sail. In the case of viscous drag of fluid in a pipe, drag force on the immobile pipe decreases fluid velocity relative to the pipe.

Drag

Drag or The Drag may refer to:

Geography

In science and technology

Drag (route)

A drag route (also known as an in route or a dig route) is a route run by a receiver in American football, where the receiver runs a few yards downfield, then turns 90° towards the center of the field and runs parallel to the line of scrimmage. This type of route is relatively safe and is thrown to an agile receiver who can make a play after the catch. Alternatively, a drag route may be used as a second option if the principal receiver on a play is covered.

The use of two crossing drag routes can also be used to try to create an open receiver by using the other receiver to block the path of a defensive back in a man coverage scheme.

Drag and drop

In computer graphical user interfaces, drag and drop is a pointing device gesture in which the user selects a virtual object by "grabbing" it and dragging it to a different location or onto another virtual object. In general, it can be used to invoke many kinds of actions, or create various types of associations between two abstract objects.

As a feature, drag-and-drop support is not found in all software, though it is sometimes a fast and easy-to-learn technique. However, it is not always clear to users that an item can be dragged and dropped, or what is the command performed by the drag and drop, which can decrease usability.

Actions

The basic sequence involved in drag and drop is:

Dragging requires more physical effort than moving the same pointing device without holding down any buttons. Because of this, a user cannot move as quickly and precisely while dragging (see Fitts' law). However, drag-and-drop operations have the advantage of thoughtfully chunking together two operands (the object to drag, and the drop location) into a single action. Extended dragging and dropping (as in graphic design) can stress the mousing hand.