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'Deflection' is a term used in physics, automotive, engineering, and weapon applications to describe four separate phenomena.

Contents

Structural engineering

Electronics

Automotive

Physics

See also

Weapons

Structural engineering

In engineering mechanics, 'deflection' is a term that is used to describe the degree to which a structural element is displaced under a load. The deflection of a member under a load is directly related to the slope of the deflected shape of the member under that load and can calculated by integrating the function that mathematically describes the slope of the member under that load. Deflection can be calculated by standard formulae (will only give the deflection of common beam configurations and load cases at discrete locations), or by methods such as "virtual work", "direct integration", "Castigliano's method", "Macaulay's method" or the "matrix stiffness method" amongst others. (See structural analysis textbooks for procedure.)
An example of the use of deflection in this context is in building construction. Architects and Engineers select materials for various applications. The beams used for frame work are selected on the basis of deflection, amongst other factors.
The elastic deflection f and angle of deflection φ (in radians) in the example image, a (weightless) cantilever beam, can be calculated (at the free end) using :
:f_B = F·L³ / (3·E·I)
:φ_B = F·L² / (2·E·I)
where
:F = force acting on the tip of the beam
:L = length of the beam (span)
:E = modulus of elasticity
:I = area moment of inertia
The deflection at any point along the span can be calculated using the above-mentioned methods.
From this formula it follows that the span L is the most determinating factor; if the span doubles, the deflection increases 2³ = 8 fold.
Building codes determine the maximum deflection, usually as a fraction of the span e.g. 1/400 or 1/600. Either the strength limit state (allowable stress) or the serviceability limit state (deflection considerations amongst others) may govern the minimum dimensions of the member required.
The deflection must be considered for the purpose of the structure. When designing a steel frame to hold a glazed panel, one allows only minimal deflection to prevent fracture of the glass.
The deflective shape of a beam can be represented by the moment diagram, integrated.

Electronics

In electronic engineering, and more specifically cathode ray tube (CRT) technology, deflection refers to the use of electromagnetic or electrostatic fields to deflect an electron beam to provide a two-dimensional display on a screen formed by the flat face of the CRT.

Automotive

Deflection as an automotive term is used as a measure of the tightness of car engine belts, which is measured using a belt gauge.

Physics

In physics deflection is the event where an object collides and bounces against a plane surface.
In such collisions involving a sphere and a plane, the collision angle formed with the surface normal (the ''incidental angle'' α) must equal the bounce angle (the ''accidental angle'' β),

See also

★ Impulse

★ Reflection (physics)

Weapons

Deflection is a tactic used in battle that describes "leading the target"; that is, shooting ahead of a moving target so that the target and projectile will collide. This tactic is only necessary when using slow projectiles, such as a crossbow bolt, or over long distances, such as in an aerial dogfight. During World War II, U.S. Navy pilots were taught explicitly on the concept in order to capitalize on the advantages of the Wildcat.