Physics of an ordinary water droplet

The video is of an effect known in fluid dynamics as the coalescence cascade, which can be observed (provided you have access to a video camera with a sufficiently high frame rate) when a drop of liquid is deposited very gently onto the surface of a layer of the same liquid.

When a droplet impacts a pool at low speed, a layer of air trapped beneath the droplet can often prevent it from immediately coalescing into the pool. As that air layer drains away, surface tension pulls some of the droplet’s mass into the pool while a smaller droplet is ejected. When it bounces off the surface of the water, the process is repeated and the droplet grows smaller and smaller until surface tension is able to completely absorb it into the pool.

 

Pretty awesome, right? In the video shown up top, the effect manages to repeat itself four times (in what scientists who study fluid mechanics call “events”) before the viscous properties of the resting pool become too strong for the smallest drops to withstand coalescing completely. MIT’s John Bush claims to have observed as many as seven such events in a row.

Advertisements

2 thoughts on “Physics of an ordinary water droplet

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s