# Physics 105 - Fall 2013 - Photo Contest Results

## Winners

### Cindy Bullock - Natural

This is a cable-stayed bridge I found near Kansas City.  A cable-stayed bridge is similar to a suspension bridge.  The biggest difference between the two bridges is the position where the opposing forces (from horizontal load) are incorporated to sustain equilibrium.   On a cable-stayed bridge there is a single tower in which cables run from different spots on the tower to the road.  The tower is responsible for absorbing all of the compression forces and the cables carry the tension. The tension of the cables must be able to hold the mass of the bridge, the additional mass of cars on the road, plus gravitational forces.  A cable-stayed bridge is not built for very long bridges because of the principle of torque.  The farther away from the tower the greater the torque becomes requiring greater tension in the cables to maintain equilibrium.  There is a point in the distance from the tower that these bridges become unsafe, due to the amount of torque. Therefore, a suspension bridge is built in situations like that since the cables are perpendicular to the horizontal force with large ground anchors on either side of the bridge.  In other words, a suspension bridge can be built for much greater distances than a cable-stayed bridge.  A cable stayed bridge is more economical and easier to build and works well for smaller distances.

### Taylor Duckworth - Contrived

Waterskiing captures the essence of centripetal force.  The physics of this sport are complicated by two different centripetal forces at play.  The first centripetal force results because the skier moves in a circular path around the boat.  As the skier moves side to side, in and out of the wake, tension between the rope and the skier keeps him moving forward.  In fact, the skier pictured accelerates as he moves around the circular path.  There is also a centripetal force between the water and the skier.  As he cuts through the water in the picture, he pushes down on the water at an angle while the water pushes back on him with centripetal force.  Even then, this turn is a side effect of the friction between the ski and the water.  Also, the spray produced by the skier comes from the force he pushes against the water. Thus, the centripetal force is a combination of the rope tension and the forces between the water and the skier.

## Honorable mentions (no particular order)

### Michael Wagner - Contrived

The four liquids from bottom to top are Water (Blue), Olive Oil (Yellow), Isopropyl Alcohol (Red), and Baby Oil (Clear). The reason that there are four levels of liquid is that each liquid has a different density. Density= Mass/Volume and has units of kg/meter^3. Water has the highest density of the four liquids at 1000 kg/m^3.  Baby oil is somewhere in the range of 750 kg/m^3. Water, the most dense, stays at the bottom and the other liquids stack up or "float" and stay on top of one another, from most dense to least dense.

### Devin Bodily - Contrived

This spinning disc is another illustration of the question about inside and outside horses of a merry-go-round that we discussed in class, except the question now is:  Is Dr. Colton's hair quicker than his eye?  The answer is "yes" when referring to linear velocity, but "no" when referring to angular velocity.  Both points move the same amount of degrees in a circle in the same amount of time, which gives them the same angular velocity.  However, Dr. Colton's hair moves a larger linear distance in the same amount of time since it makes a bigger revolution, therefore it is has larger linear velocity and is more blurry than images closer to the center.  This is more dramatically illustrated by noting the difference in acuity between "DIZZY" written in the center and "DIZZY" written on the outside.  Let's hope, for Dr. Colton's sake, that his hair slows down and he doesn't lose it.

### Devin Bodily - Natural

After a heavy snowfall the branches of this pine tree were weighed down with snow. Suddenly, snow starts to fall off and the branch pops back up.  Before this happened, the downward pull of gravity on the snow and the branch was obviously in equilibrium with the force of the branch pushing up so one would think there must have been an outside force that caused this motion.  In some cases it may be caused by wind, but it also could be caused by chunks of partially melted snow slipping through the cracks of the branch.  If the loss of weight is large enough, then the upward force of the branch will suddenly exceed the downward pull of gravity and the branch will elevate quickly, throwing chunks of snows everywhere.  This is most likely to happen on the end of a branch where the branch is smallest and the greatest torque is being applied (torque = perpendicular force x distance from axis).  When this large force is suddenly lost, the results are dramatic.

### Jacob Parmley - Contrived

On my mission we would use the lining of a tea bag to teach lessons about the Holy Ghost and how being baptized by fire can lift us higher.  Here is as picture of a tea bag right after lift off.  We all know that hot things rise, but the question is why.  Hot air balloons capture hot air which is less dense than the air around the balloon, causing it to rise.  Here, however, we don't have something catching the hot air being given off, but there is an upward draft being made.  As the tea bag burns, the air around it begins to increase in temperature.  As it becomes hotter, and less dense than cooler air, the air lifts up and is replaced by cooler and denser air.  This thermal convection causes an upward draft right around the tea bag.  As the tea bag burns, it loses mass and eventually becomes "light" enough that the upward draft has enough force to lift it up into the air.

### Kelsey Mathews - Contrived

This photo was taken when I went skydiving in October. At this moment, the parachute had just been pulled applying a force against gravity to slow our acceleration toward the Earth. Before the chute was pulled, we were in free-fall, and the only force acting on us was the force of gravity pulling us towards Earth’s surface. After the chute was pulled, we had a counter-force against the gravitational force. Since it was an abrupt change, it caused our faces to become distorted. If you look at other pictures during the jump, this was the only time our faces were distorted.

### Stephanie Hiltscher - Contrived

Before taking this picture I thought that getting hit in the side of the head by a snowball (which my cousin was willing to be subjected to), would demonstrate an inelastic collision in which the snowball lost all kinetic energy and stuck to my cousin Alec's face; however, this was not the case. Because the snowball was made with powder snow, the collision was partially elastic with snow particulates flying in the forward direction and some in the upward and downward directions. I loved how visual this example proved to be in regards to a collision with partially conserved momentum.

### Matthew Royster - Contrived

This was a picture I took on my way to Utah. This picture demonstrates one of Bernoulli’s Principles associated with lift. This helps demonstrate how airplanes are able to fly. At this moment the air is moving faster over the top of the wing because the wing is curved and this creates a lower pressure on the top. The air is moving slower under the wing which creates a higher pressure on the bottom of the wing. The pressure difference creates a net aerodynamic force, pointing upward and downstream to the flow direction. This means that the airplane is literally pushed up, allowing it to fly.

### Kevin Kemp - Natural

A cold wet winter storm kindly washes the Herald B. Lee Library windows this past Wednesday.  With water trickling down from melted snow above and a hard night’s freeze, heat energy is removed creating a beautiful array of ice crystals.  This demonstrates energy change in thermal processes.  The original heat received from the sunlight and building left the water as night time came and the temperatures plummeted.

### Taylor Duckworth - Natural

Taken in the mountains of South Korea, this picture exhibits the natural summation of forces that occur in a suspension bridge.  Tension in the cables is supports the weight of the deck of the bridge and anything that crosses its path.  In order to prevent too much tension being focused on one of the vertical cables, a cable runs horizontally and anchors itself to the walls of both sides of the ravine.  The anchorage in those rock walls support the tension in the cables and counteract the gravitational force that would cause the bridge to fall down below.

### Mark Lahtinen - Contrived

The watch pictured is classified as having mechanical movements. The movements of mechanical watches are based on potential and kinetic energy. When the watch is wound, the main spring is given the spring potential energy that the watch needs to overcome the forces of friction and wind resistance. The most important part of a watch to keep time lies in the balance wheel. This wheel rotates at a specific rate of two cycles per second. It is attached to a small spring, called the hairspring, which oscillates at this very predictable pace. Because of this predicable pace, the watch is able to accurately keep time. An oscillation diagram for the hairspring can be drawn based on time and angular distance, which will have a frequency of two cycles per second, intersecting at precisely the one second mark. The spring converts spring potential energy to angular momentum. The angular momentum is then converted back into spring energy, which allows for the predictable oscillations of the balance wheel. The balance wheel acts on a part called the pallet, which in turn acts upon the escape wheel four times a second. The escape wheel is linked to the second hand of the watch, which has four small movements that are equivalent to one second on the face of the watch. The second hand in turn acts upon the other hands of the watch to fulfill its purpose and keep time. See my watch in action!:  //www.youtube.com/watch?v=W-9VjOWyFD0&feature=youtu.be

### Tyler Condie - Natural

This past summer I backpacked through Europe with two friends and still to this day I remember the sunset that we witnessed in the Netherlands.  Specifically that which was so mesmerizing was watching the waves in the ocean as sailboats passed by one after the other.  Physics explains that as two waves with a given amplitude collide with each other that the amplitude of the resulting wave will be equal to the summation of both waves.  This is an example of constructive interference.  Other waves we watched which were not in phase with each other were examples of destructive interference and essentially would cancel each other out if each wave were of similar amplitude.

### Christian Boekweg - Contrived

Anti-gravity has been something that scientists and science fiction writers have dreamed about since H.G Wells wrote about "Cavorite", a gravity blocking substance in his book The First Men in the Moon. Anti-gravity is a place or object that is free from the force of gravity. It is not the feeling of weightlessness that one experiences in free fall, as we learned in class Nor is it a balancing for that counteracts the force of gravity. I took a photo that clearly demonstrates a fact that has evaded scientists and has become apparent to virtually every missionary in the world.  That is the discovery of a graviton in the hallways of the Provo MTC.

(Humor trumped the lack of physics explanation. – Dr Colton)

### Ryan Carlson - Contrived

This is a photo of ball collisions on a pool table. The photo was taken using a one-second shutter speed and shows the paths of seven balls in that one-second interval. The comparative speed of the ball can be determined by looking at the length and solidity of the line. The colored balls remained in the same position until the cue ball made impact. You can slightly make out the path of the cue ball before it struck the other balls, which is an indicator that the cue ball was moving fast before it struck. After impact, its momentum was transferred to other balls in a series of elastic collisions. The cue ball actually reverses directions. Each of the balls acquired translational kinetic energy and rotational kinetic energy. The cue ball developed horizontal rotational energy as noted by its curving motion after impact, which was cool.

### Travis Johnson - Natural

This photo of the sunset at Huntington Beach in California shows us the beauty of the earth. Not readily viewed in these types of pictures are the physics involved, as the observer of the sunset walks into the glow of the sun, she leaves footprints in the sand, a lasting memory of where she once was. These footprints represent a common topic discussed in physics, that of pressure. The footprint is created by the pressure of the foot being placed on the surface of the sand, the larger the surface area of the object hitting the sand, the less deep the print will be. Mass will also affect the deepness of the print. A human foot has an adequate mass and surface area, enough to imprint in the sand a footprint that will last, until disturbed by some other means.

### Kate Strickling - Contrived

This photo was taken in Moab during a rally race that my friend and I participated in (he was the driver, I was a passenger). This photo depicts the physics of a rally turn. The physics of racing on dirt is very different from racing on a paved track. Rally car drivers use a car’s mass and momentum to turn on loose surfaces. The driver uses the brakes to shift the car’s weight and uses momentum to turn the car. Steering is minimal. To turn the car on a loose surface where the coefficient of friction is much smaller, the driver uses the brakes to shift the car’s weight forward. This puts more mass over the tires, creating more grip. While the coefficient is still small, the increase in mass creates more force pushing down on the dirt and helps the car to not drift off the track.

### Ben Curd - Contrived

The photo was taken in Afghanistan after a random conversation with our explosive ordinance disposal team (EOD) about how only cool guys walk away from explosions. Unbeknownst to us, this drove the EOD team leader insane trying to figure out how to create a "fire-wall" for a photo prior to completing his deployment.  He finally figured it out by filling several trash bags with about 5-litres of diesel fuel, then placing the bags on top of evenly spaced coils of detonation cord (a type of explosive that detonates simultaneously across the entire length of the cord).  The physics of this system works because just like in collisions, the two objects involved (the earth and the bags of fuel)  encounter the same force for the same amount of time directed in opposite directions. Since the masses of the two objects are unequal (obviously the earth has more mass than a 5-litre bag of diesel fuel), then they will be set in motion by the explosion with different speeds. Yet despite the different masses the momentum change of the two objects (mass x velocity change) will be equal in magnitude and opposite in direction.  Therefore the fire/explosion "blows-up."  The photo is of my platoon, I am standing to the left of the black guy in the picture.