Session 56 . - . 3:30-4:20 pm . - . Dakota G

SD-AAPT Photo Contest & Annual Meeting

Hydrophobic Flower

Catching Fire

Hydrophobic Flower First Place

In this photo I made a flower out of hydrophobic sand and put water droplets on it. Hydrophobicity occurs when the functional group of a compound is nonpolar. The molecule becomes hydrophobic when a nonpolar molecule is attached to the end of the compound. So if the compound’s surface comes in contact with the water, the water will slide off because there are no attractive forces shared between the two surfaces. The surface tension of the droplets creates a very round drop instead of a flatter drop. On a hydrophilic surface, it “hugs” more of the water because the surface is water loving, but on the hydrophobic surface it is different. The internal contact angle on the hydrophobic surface increases because the cohesive forces between the water molecules make it take on a spherical shape.
It was not until I printed this picture that I noticed the water droplets on the hydrophobic sand create a convex lens and magnify the sand under the droplets. The water droplets then create a magnified virtual image. When the object is between a convex lens and its focal point, the light rays from the object diverge when they pass through the lens. The brain interprets these diverging rays as coming from an object directly along the path of the rays that reach the eye. This creates a magnified virtual image on the same side of the lens as the object.

"Catching Fire"(Natural) Second Place

This picture was taken as water droplets fell from an icicle into a sunset. This is an example of total internal reflection. When the light hits the drops of water, it is bent due to differences in the refractive index between water and air. Once in the drop, a portion of the light is unable to cross the water/air boundary and is reflected back internally. This light cannot escape since the angle of incidence is greater than the critical angle. The result is dripping "fire".


Laser Mania

Mouse Trap Car Third Place

A mousetrap car is a small vehicle that is powered by the spring of the mousetrap. The mousetrap car utilizes a lever, a spring, and wheels and axles. When the mousetrap is set and a string is wound around the axle, the car has elastic potential energy. When the trap is tripped the elastic potential energy of the spring is converted to the rotational movement of the lever arm that is attached to the spring. Fishing line is connected to the end of the lever arm and is wrapped around the back axle. As the lever arm moves around the arc of the spring it pulls on the fishing line applying a torque to the axle. The axle is connected to the back wheels. Strips of a balloon are wrapped around the back wheels to supply the friction to get the car going. As the spring releases, the elastic potential energy is turned into kinetic energy, which moves the car forward. Once the trap has snapped shut and the string is unwound from the axle completely, the momentum of the car keeps it moving forward until friction between the wheels and the floor and air resistance cause it to stop.

Laser Mania

In this photo I setup a laser tank with water and pine sol. I used a green laser to demonstrate total internal reflection. When I first looked at the tank with the laser we saw that the light bounced off the walls of the tank, making a zigzag. It made the zigzag pattern because the ray had a angle of incidence greater than the critical angle. You can see this zigzag pattern in the photo. When I looked from the top of the tank I saw a standing wave pattern. I was surprised to see the round edges instead of the zigzag I saw below. The round edges of the standing wave must be caused by the changing angle of incidence as the laser zigzagged across the tank getting closer and then further away from my eye. As the light went from the water to the air, the refraction of the light waves created the round edges. Also, the reflection off the glass helped create the standing wave pattern. I found this out by putting a pen in the path of the laser, which showed that the other side of the standing wave was a reflection off the glass.

Bailey Eidahl.JPG

Alison Murphy.JPG

Water Physics

The picture that was taken shows the reaction that takes place when a water droplet drips into a pool of water. When the water droplet lands in the pool of water, it creates a depression which then comes back up to form a peak shown in the picture. This depicts one of Isaac Newton’s three laws of motion; every action has a equal and opposite reaction. The action in this picture would be the water droplet creating a depression, and the reaction is shown once the water comes back up to make a peak.

Specular Reflection

Specular reflection is the reflection off of a smooth surface such as a mirror, a window, or a calm body of water. When a ray of light is reflected from a smooth surface, the angle of reflection is the equal to the angle of incidence. A simple way of understanding this law is to think of the image as an array of individual light rays traveling parallel to each other, when the array of light rays strike a smooth surface the light rays reflect and remain concentrated in the same array leaving the surface giving the appearance that the same image is sitting on top of the water.

Chantell Newton.jpg

Emma Schmidt.JPG

Spider webs

Spider webs are lightweight structures that are believed to uphold better than the top grade steel. These structures have been seen since the Jurassic period- or even sooner. They resist wind, insect impact, and can catch prey even when threads are broken. Spider webs are generated from spiral and radial threads. Radial web radiates out from the center of the web as spiral threads connect everything in the familiar circular pattern. It has been proven by research that radial threads are significantly stronger than spiral threads- in the sense of greater thickness, chemical composition, and microscopic structure. With less knowledge about the mechanics of web making, it has been concluded that orb webs have beneficially evolved due to natural selection.
Looking more closely at each individual thread, the silk consists of basic proteins- which are called beta sheets. When stress is applied to a strand the responds in a nonlinear fashion which cause the sheets slide across each other and eventually ruptures when 67% of max force is applied. Light stress triggers a more uniform way of coping by spreading the load across the web. Continuing force makes thread become thicker until breaking point.
When tension is applied to a certain area of the web, it is evenly distributed throughout until passing off into the outmost threads. With controlling the strength with added threads, spiders can thrive in various given environments. For those who prey on small insect, they attend to make structures denser.
Applied knowledge shows that with elastic materials, force becomes redistributed when damage occurs which weakens overall. Spider webs have the same thought, but when one thread is broken, the rest of the web is unaffected. Damage tolerance is because of its hierarchical design- that is becoming motivation for engineers.

Physics Behind Pool

Many people believe the classic game of pool is a matter of angles and inches. In a sense, it is; however, there is also a law of physics between each hit of the ball. Newton’s Third Law of Motion is the basis behind how a ball reacts when it comes in contact with another ball.
Newton’s Third Law of Motion states that for every force there is an equal and opposite force. In pool, when the cue ball hits another ball, the force behind the cue ball will apply to the ball it comes in contact with, which causes the contacted ball to continue in the direction the cue ball was hit. On the other hand, once the cue ball contacts another ball, an opposite, but equal force will act on the cue ball, which would cause it to stop where contact was made or bounce back in the direction it came from. As shown in my picture, the cue ball has contacted the racked balls and the blur on the cue ball shows that the rack of cue balls has exerted an opposite force on the cue ball that has sent it back from the direction it came.
Also, my picture portrays the force that was exerted upon the racked balls by the blur of the ball. The black, green, and purple balls are clear because the forces exerted on them from both sides are equal, causing them to stay in place. However, the balls on the edge of the rack are moving outward because of the force put forth upon them from the cue ball. The nine, twelve, and fifteen balls are traveling to the side because they have come in contact with the balls moving outward, which bounces them off to the side.
Overall, physics is a key component in the game of pool. With a clear understanding of Newton’s Third Law of Motion, anyone can become a competitive pool player. Depending on how far the ball needs to travel, one can predict the amount of force to put behind the cue ball in order for it to transfer the right amount of force on to the target ball to send it into the desired pocket.

Jacey Brunsen.jpg

Laulima Russell.JPG

Formation of Ice Crystals

The picture I took it when ice crystals formed on an iron fence. Ice Crystals start to form at 0o C, and lower, from water vapor in the air and depending on the temperature and humidity is how the shape and pattern of the crystals will turn out. The ice crystals mainly try to hit a surface that is able to sustain the low temperature for example an iron fence like in the picture. Ice crystals then expand but depending on temperature and the air because if it is cold and the air is dry it will take longer for the ice crystals to form.


There are a lot of everyday materials that fluoresce, or glow, when placed under a black light. A black light gives off highly energetic ultraviolet light. You can't see this part of the spectrum, which is how 'black lights' got their name. Fluorescent substances absorb the ultraviolet light and then re-emit it almost instantaneously. Some energy gets lost in the process, so the emitted light has a longer wavelength than the absorbed radiation, which makes this light visible and causes the material to appear to 'glow'. Fluorescent molecules tend to have rigid structures and delocalized electrons. Examples of common materials that hold florescent molecules are: white paper, petroleum jelly, U.S. $20 bills, tonic water, laundry detergent, and jellyfish.