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
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
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.
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
- 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.