Deflection

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

Contents 1 Structural engineering 2 Electronics 3 Automotive 4 Large Diesel Engines 5 Physics 5.1 See also 6 Weapons

Structural engineering

Deflection (f) in 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 may be measured using a belt gauge. Practically, one applies inward pressure to the belt in the middle of the span between two pulleys. The amount that the belt can be moved from its static position ("deflected") will be an indication of the belt\'s tension. The total amount of deflection will also be influenced by the force applied, the distance between the pulleys, as well as the elasticity and overall length of the belt.

Large Diesel Engines

To take Deflections is the recording of the alignment of Crankshaft bearings by measuring the distance between the crank webs, using a clock gauge, as the crankshaft is rotated. The greater the deflection recorded, the greater the mis-alignment or weardown of the Main bearings.

Physics

Deflection occurs when an object hits a plane surface

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), $\backslash alpha\; =\; \backslash beta$

Magnetic Deflection refers to Lorentz forces acting upon a charged particle moving in a magnetic field.

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.

Leading targets is the practice of aiming one\'s weapon ahead of his or her target so that the projectiles will hit their mark. Over reasonably short ranges, leading is typically unnecessary when using firearms, but it is still relevant for sniping (where the bullet may take a second or more to hit its target), as well as for weapons such as bows that use lower-velocity projectiles. It is generally unnecessary for guided projectiles, although the guiding mechanism may lead its targets by itself.

Modern computer games of the first-person shooter genre typically feature a number of relatively low-velocity projectile weapons, such as unguided rocket launchers, so leading targets is relevant to them as well. Additionally, even for high-velocity or hitscan weapons, there are issues of latency that require leading in some multiplayer games. Essentially, even if the shooter has the target exactly in his sights, by the time the shooter\'s computer finishes informing the server that he has fired, the target may have moved enough to avoid the shot.

QuakeWorld and the Source engine, among others, use a lag compensation system which moves all players back to a point in time based on the shooters client interpolation time and ping. Such systems eliminate the need to lead hitscan weapons, but introduce the risk of players perceptibly being shot after taking cover.

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