Matt Kuchta and I have been working on several projects involving our sparkly new high speed camera. One thing we are looking at is dropping objects into fluids and looking at the fluid dynamics involved. Here is an interesting video that Matt shot earlier today.
The fluid flow up the ball looks to be moving quite quickly so I decided to fire up Tracker to look at the video. Let me tell you something – you have no idea how amazing it is to mix Tracker with a high speed shot.
The best part is the Autotrack feature; you pick an edge or feature on the moving object and Tracker will mark the location in each frame. It works really well. Hat’s off to Doug Brown, creator of Tracker.
Here’s what we see.
The ball itself is falling at about 3.4 m/s, but the water is sliding up at over 5 m/s. It is interesting the the sphere doesn’t appear to slow appreciably as it enters the water. Of course it is a little more difficult tracking the motion at that point so I’d like to revisit that point later.
So the water is in fact moving up faster than the ball is falling! This really begs the question what is forcing the water up and around the sphere. Is it a result of surface tension, boundary layer effects, or some other fluid phenomena? Anybody have suggestions?