The behavior of bubbles with radii of 0.5-0.7 mm rising through water in the presence of a solid boundary were observed using a high-speed video camera. Fluid inertia and surface tension cause a bubble to bounce several times from a horizontal wall before viscosity dissipates the energy. An energy balance involving the kinetic energy of the fluid motion, the surface energy of the air-water interface, and the gravitational potential energy aids in the interpretation of the dynamics of the collision. We also observed the motion of a bubble rising under an oblique wall with an angle of 10 degrees-85 degrees to the horizontal. When the angle was less than about 55 degrees corresponding to We<0.4, the bubble slid steadily along the wall. At steeper angles the bubble was observed to bounce repeatedly from the inclined wall without any apparent loss of amplitude. It was also determined that the critical Weber number of coalescence of a bubble rising toward a stationary bubble is 1.6. At Weber numbers below this critical value, the two bubbles coalesce on impact while bubbles bounce at higher Weber numbers. (C) 1997 American Institute of Physics.
