The air in a cloud is always moving around. This causes some of the droplets to bump into others. (1) The bumping droplets join together, forming larger droplets.

云中的空气总是在移动着。这便引起一些水滴相互碰撞。相互碰撞的水滴结合在一起，形成更大的水滴。

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It swims and is affected by pushing and bumping air and pushing and bumping water that creates swirling.

它会滑行，并受到空气推挤和冲撞的影响，这种推挤和冲撞就造成了水漩涡。

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The powder gas, generated continuously due to burning of propellant forms air-cushion among propellant grains, which can buffer and protect propellant grains from bumping, impacting and extruding.

发射药燃烧时不断产生的燃气在药粒之间形成气垫，对药粒的撞击、挤压起到缓冲保护作用。

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Meteorologists were blaming the nor'easter on the collision of two storm systems: cold air traveling south from Canada bumping into a moist low pressure system heading north from the Carolinas.

WSJ: Major Blizzard Bears Down on Northeast

They enliven their gait by bumping each others' hips rhythmically and leaping into the air as they walk.

UNESCO: Culture