High-Speed Photography

High-speed photography enables one to investigate events that happen too quickly to be studied in detail. Slower examples are water splashes and insect flight, both of which I've investigated. Racquetball collisions and balloon pops happen even more quickly, and some of the fastest events are bullet firings and hydrogen balloon explosions, both of which have been investigated by high school students at the NC School of Science and Math.

I began learning about high-speed photography in August 1999, after I left NCSSM. If you're interested in learning high-speed photography, you'll be glad to know that it's easy and not at all expensive. Check out the website HiViz.com, which is the most thorough and informative website on high-speed photography I have found. It will be great to get you started. Also check out the links at right.

Splash Modeling

After seeing many different kinds of splashes and ball collisions, I found that generally, impacts of solids at high velocities resemble impacts of liquids at low velocities. When these impacts result in a splash, the shape of the splash seems to depend on factors such as whether a tough skin exists on the material (a basketball vs. a milk drop) which could be likened to surface tension, the stiffness or elasticity of the material, perhaps the viscosity of the liquid if we're dealing with a liquid, the impact velocity, and possibly other factors.

I'm interested in determining how the shape of a splash depends on the above parameters. I'll need to photograph lots of splashes and take data from the photos in order to come up with a good model. Eventually I'd like to write equations that would describe the splashes, and to be able to simulate any kind of splash on a computer by just adjusting the input parameters.

Observations I've Made

• A milk drop falling into a small film of milk on a hard surface will create a splash that forms a crown, with waves rippling outward from the collision.

• A squish ball colliding with a wall will deform dramatically, with ripples traveling over its skin away from the direction of the ball's travel.

• A racquetball, which is less flimsy than a squish ball, will similarly deform. However, a higher impact velocity is needed to show the same extent of deformation as a squish ball at a lower impact velocity.

• A basketball will also similarly deform, but an even higher impact velocity is needed to overcome its stiffness and cause it to deform.

• A golf ball should theoretically show the same deformation, but I think that due to its high stiffness it would shatter before its surface rippled like that of a squish ball.

• A meteorite is a very rigid piece of material, but when traveling at incredibly fast velocities it creates a splash on the Earth's surface that very much resembles a milk drop splash. The meteorite acts much like the golf ball, likely shattering upon impact, but the solid Earth is very pliable at the high impact energies involved. The solid ground seems to behave like a liquid unbounded by any kind of skin, forming a crown as waves ripple across the Earth's surface from the point of impact.

• An egg has very low elasticity. When it collides with a wall, the resulting splash doesn't even form a crown. The splash mostly travels outwards, perpendicular to the direction of motion before impact. There's not enough energy in the impact to cause waves to ripple across the wall from the impact point.