# Deflection (physics)

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{{Short description|Change in a moving object's trajectory due to a collision or force field}}
{{refimprove|date=November 2025}}
{{Use dmy dates|date=January 2025}} 
thumb|upright=1.35|An object hitting a surface is an example of deflection.

'''Deflection''' is a change in a moving object's [velocity](/source/velocity), hence its [trajectory](/source/trajectory), as a consequence of contact ([collision](/source/collision)) with a surface or the influence of a [non-contact force](/source/non-contact_force) [field](/source/Field_(physics)).<ref name=EduTinker>{{cite web|url=https://edutinker.com/glossary/deflection/|website=EduTinker|title=Deflection|date=October 31, 2023|access-date=November 7, 2025}}</ref> Examples of the former include a ball bouncing off the ground or a bat;<ref>{{cite book|url=https://books.google.com/books?id=K218AgAAQBAJ&pg=PA243&dq=%22Deflection%22+baseball+-wikipedia&hl=en&newbks=1&newbks_redir=0&source=gb|pages=243-247|title=Projectile Dynamics in Sport: Principles and Applications|first=Colin|last=White |year=2010|isbn=9781134027620|publisher=Taylor & Francis|access-date=November 7, 2025}}</ref> examples of the latter include a [beam of electrons](/source/Cathode_ray) used [to produce a picture](/source/Cathode_ray_tube),<ref name=EduTinker /> [quantum deflection](/source/Delbr%C3%BCck_scattering),<ref>{{cite journal |url=https://physics.aps.org/articles/v16/s114|title=Quantum Deflection Unraveled|date=August 8, 2023|journal=Physics|volume=16|page=s114|first=Ryan |last=Wilkinson|access-date=November 7, 2025}}</ref> or the [relativistic bending of light due to gravity](/source/General_relativity).<ref>{{cite web|url=https://physics.stackexchange.com/questions/768088/newtonian-light-deflection|website=Physics Stack Exchange |title=Newtonian light deflection|access-date=November 7, 2025}}</ref>

==Deflective efficiency==
{{see also|shock (mechanics)|perfect mirror|absorption (electromagnetic radiation)}}
An object's '''deflective efficiency''' can never equal or surpass 100%, for example:
*a mirror will never [reflect](/source/Reflection_(physics)) exactly the same amount of light cast upon it, though it may concentrate the light which is reflected [into a narrower beam](/source/concave_mirror).
*on hitting the ground, a ball previously in [free-fall](/source/Free_fall) (meaning no force other than [gravity](/source/gravity) acted upon it) will never bounce back up to the place where it first started to descend. 

This transfer of some energy into heat or other radiation is a consequence of the theory of [thermodynamics](/source/thermodynamics), where, for every such interaction, some energy must be converted into alternative forms of energy or is absorbed by the deformation of the objects involved in the collision.

== See also ==
* [Electrostatic deflection](/source/Electrostatic_deflection)
* [Coriolis effect](/source/Coriolis_effect)
* [Deflection yoke](/source/Deflection_yoke)
* [Impulse](/source/Impulse_(physics))
* [Reflection](/source/Reflection_(physics))

==References==
{{reflist}}

==External links==

Category:Scattering
Category:Collision

{{scattering-stub}}

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Adapted from the Wikipedia article [Deflection (physics)](https://en.wikipedia.org/wiki/Deflection_(physics)) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Deflection_(physics)?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.