# Motion

### Notes on the Physical Science Final Exam

Grades are in. So, let me just say a couple of trends that I saw on the physical science final exam. Gravity on the moon I asked the question: "why is the gravitational force on an astronaut less on the moon than on Earth?" The simplest answer is that the gravitational field on the moon is smaller than on Earth (I would accept that answer). Why is this? It is because the moon as a much smaller mass even though it also has a smaller radius (that idea is rather complicated for this class - that gravitational force depends on both mass and radius). I would also take "the mass is smaller" as…

### When Fluids Collide

Fluids are a constant source of inspiration for high speed photography. Water and milk are two of the common liquids around us every day, but still their complex behavior is a source of wonder. Fluid scientists are still pioneering some of the basic equations that are responsible for the complex motion of fluids. In these pictures a drop of liquid is falling into a container of liquid. The first falling drop creates a recoil splash that shoots up out of the container. Just when the recoil droplet gets to the top of its motion a second falling droplet collides. The timing often happens…

### How do you photograph a bad day?

This is how. ----------- This image was provided by Ted Kinsman for Photo Synthesis.

### So this Bullet Runs Into an Egg...

With high speed photography, I can use a high voltage spark to create a flash of only 1/1,000,000th of a second in duration. The problem is that there are not a lot of things that move this fast that such a flash is required to stop the motion. Bullets are such a subject requiring a very high speed flash system. Around the lab we jokingly call this "ludicrous speed". After photographing bullets hit just about every conceivable object it is time to move on to other subjects. In this case a paint ball is sent into the edge of a straight razor blade. The paint ball crosses two optical…

### Juggling Fire

I have photographed jugglers several times in the past for physics text books. I have been impressed with the level of skill some jugglers can obtain. It is difficult enough to juggle three balls, four is more difficult, and fire is a another story. When objects move in a circle they can undergo some fairly complicated motions. What would be the best way to show this motion in a still image? In this case the camera is panned by the juggler at a constant rate on a computer controlled pan head. When the juggler is about the center of the frame a flash is set off. The image shows…