  Oblique collision of solid particles with surfaces has been a topic of
extensive study in Newtonian mechanics, which also explains the motion of
bubbles and droplets to some extent. Here, we observe that air bubbles exhibit
a backflipping behavior when they collide with a tilted surface. Our
experiments reveal that bubbles with radii 0.6-0.7 mm undergo backflipping when
they collide with surfaces at an angle of up to 15^o with the strongest
backflipping at 3^o. Particle image velocimetry reveals that the backflipping
behavior is caused by wake-induced circulation around the bubble, which applies
a lift force on the bubble. We develop a theoretical model that incorporates
potential flow theory to characterize the circulation caused by the interaction
between the bouncing bubble and its wake. The theoretical results are in good
agreement with the experiments confirming the key role of the wake-induced lift
force in backflipping. Finally, we show that the backflipping behavior of air
bubbles can be leveraged for sustainable cleaning of a biological surface
coated with a protein solution.
