Hop-up {{cite book, author=Kovacs Bloomfield, title=Airsoft! How to Win an Airsoft War: Secret Tactics for Success Revealed!, url=https://books.google.com/books?id=Y8tuufbh_NAC&pg=PA20, date=1 March 2012, publisher=Ebook.GD Publishing, isbn=978-1-61323-030-5, pages=17–20 is the

backspin In racquet sports and golf, backspin or underspin refers to the reverse rotation of a ball, in relation to the ball's trajectory, that is imparted on the ball by a slice or chop shot. Backspin generates an upward force that lifts the ball (see M ...

put on

airsoft Airsoft is a team game in which participants eliminate opposing players by tag (game), tagging them out of play with airsoft pellets, spherical plastic projectiles shot with mock air gun, air weapons(usually powered by an electronic motor) call ...

pellets and BBs to increase their range via the

Magnus effect The Magnus effect is an observable phenomenon commonly associated with a spinning object moving through a fluid. The path of the spinning object is deflected in a manner not present when the object is not spinning. The deflection can be expl ...

. Hop-up devices apply backspin to the projectile reducing the air pressure on its top side. This causes the plastic pellet to fall less over a given distance than it would without the spin applied, extending the effective range of the weapon without increasing velocity. In airsoft guns, this is usually implemented as a projection (called a bucking) into the path of the projectile, on the top of the barrel. The bucking momentarily hinders the top side of the projectile, imparting a backspin that can exceed 1,000 rpm (17 rotations per second). This is usually adjustable so that the effect can be tuned to suit the weight or speed of the projectile and each player's preference. The primary cause of the lift is the

. There is a layer of non-moving air (the

boundary layer In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces a no-slip boundary condi ...

) on its surface. In the case of a spinning ball, this layer gets thrown off at an angle. Newton's laws state that in order for air to be thrown in one direction, the ball has to move in the opposite direction. According to the Magnus explanation, the rotating ball would throw air downward and to the rear, thus giving lift. The boundary layers on the top and bottom separate unevenly, creating a wake that is lower than the middle of the ball, appearing like a comet's tail pointing down. This can be verified in

wind tunnels Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...

and is well documented in

fluid dynamics In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids— liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) an ...

textbooks A textbook is a book containing a comprehensive compilation of content in a branch of study with the intention of explaining it. Textbooks are produced to meet the needs of educators, usually at educational institutions. Schoolbooks are textbook ...

References

Airsoft Pneumatic weapons