Rainbows are one of the most famous and beautiful phenomena in our Hawaiian Islands, and anybody who grew up here has seen the brilliant bands of light over the Ko'olaus or above Diamond Head. But what is a rainbow? Simply put, we've learned that a rainbow is a product of light refraction, as the white light from the sun behind the viewer passes through the raindrops and is diverted to the viewers eyes. The reason the rainbow makes a "bow" shape is because the Earth blocks a good deal of the sun's light, resulting in the semicircular arc form the light that does pass the Earth.

Visual aids helped me to understand this concept more fully. The following section is taken from the University of Carolina's website:

-

-

The traditional diagram to illustrate this is shown here as adapted from Humphreys, Physics of the Air. It represents the path of one light ray incident on a water droplet from the direction SA. As the light beam enters the surface of the drop at A, it is bent (refracted) a little and strikes the inside wall of the drop at B, where it is reflected back to C. As it emerges from the drop it is refracted (bent) again into the direction CE. The angle D represents a measure of the deviation of the emergent ray from its original direction. Descartes calculated this deviation for a ray of red light to be about 180 - 42 or 138 degrees.

-
-

It was this understanding of the physical aspects of rainbows that helped me to explain the following picture, taken from Kailua Beach near sunset:

It looks like a little patch of rainbow floating out over Flat Island. I though of two possible explanations for this phenomenon, and in reality it could be both. The first is that there are only water droplets in the air (rain) at that one spot. The second is that the setting sun is being blocked by some landscape feature, most likely the Ko'olau mountain range, and only that relatively small section of sky is receiving direct sunlight. In both cases, the sun is setting behind the camera, which meshes with the UCar diagram above. This is a cool picture made evn cooler by an understanding of physics!!1! :D

Blue Angels

A while ago the Blue Angels were in the islands, and I had the opportunity to go watch them perform their tight formation flying. As I watched in awe as the jets screamed overhead, I realized that they were creating sonic booms! This is because the jets were flying faster than the speed of sound (which varies according to temperature but is usually around 343 m/s), creating the amplified sound waves we call sonic booms. IT WAS AWESOME!!

I also got to thinking about the medium affecting the velocity of sound. Since sound actually travels relatively slowly through air when compared to other mediums, creating a sonic boom in another medium (underwater, for example) would require far greater speed. In addition, an underwater sonic boom would probably result in physical waves as well, and a large enough one could theoretically cause a tidal wave or similar large disturbance. Perhaps sound could be used for underwater demolition without causing harm to the local ecosystem! THE POSSIBILITIES ARE ENDLESS! SCIENCE RULEZ!!!1!!

Physics Blog 8: Torque

Recently I went to one of my brother's kayaking races and was struck by the physics concepts that I witnessed!!

A kayaker

I noticed that kayakers spread their hands out when gripping the paddle. At first I wondered why they didn't just keep both hands together in the middle, as that would accomplish the same motion. However, I quickly figured out that this was a matter of TORQUE!! By spreading the grip apart, the kayaker increases the lever arm (r), which in turn increases the torque he can apply (T) given the equation T=Fr where F is the force. I am beginning to understand just how much physics applies to sports - understanding the physics behind certain actions can give more of an edge than raw strength. PHYSICS RULEZ!!!

Physics Blog 7: Uniform Circular Motion

Uniform circular motion, though it may seem an abstract concept in class and on our worksheets, is actually all around us. It was even abundant during Homecoming Week. On the day to dress up as pirates and ninjas, I was a ninja equipped with a deadly pair of NUNCHAKU!! (the plastic kind you buy at Price Busters for like $1) I now realize that swinging my nunchucks over my head was creating UNIFORM CIRCULAR MOTION!!

It's hard to tell from the angle of the picture, but the foam nunchucks are probably swinging at a slight angle below the horizontal. This makes the center of rotation just a little below the top of the half I'm holding. The centripetal force is being provided by the tension in the string, which is clearly less than the string's maximum tension - otherwise it would break. The length of the string is also the hypotenuse of an imaginary right triangle, the horizontal leg of which is the radius of the circle of motion. If I knew the length of the string (L) and the angle below the horizontal (A), I could calculate the radius (r) using r = (cosA)/L. If I were also given the linear velocity of the nunchucks, I could calculate the angular velocity using v = rw. PHYSICS IS ALL AROUND US!! :D

Physics Blog 6: Collisions

I was thinking about collisions in real life when I saw the perfect topic for my blog on TV: the Texans vs. Titans game! I was going to go find some footage of tackling in football when Cortland Finnegan and Andre Johnson provided me with all the footage I needed:

Collisions

When the punching starts, Andre Johnson's fist clearly has more momentum than Cortland Finnegan's face, as Finnegan's head bounces back every time Johnson strikes him. This means that, since the equation for momentum is p=mv, Johnson's fist has either greater mass or greater velocity - in this case, it is less massive than Finnegan's head and therefore must have far greater velocity. Additionally, both players exert enough force to overcome the friction between each other's heads and helmets and tear the helmets off at the onset of the fight. It's exciting to see physics concepts at work!! :)

Physics Blog 5: Picture Poses

This past week was Homecoming, and there were probably hundreds of possible topics for blogs. However, I really noticed physics at work when we were taking a group picture:

You can see on the right hand side that my friends Val and Andrew and I were holding Kevin motionless in the air. To achieve this, we had to offset his weight with the force we were applying from beneath him, and since he was not touching the ground, our three forces combined had to equal what the normal force would have been. If you look at other people in the picture, you can see other examples of the normal force being replaced with an equal force. PHYSICS IS FUN!! :)

Physics Blog 3: Hiking

A couple weekends ago I was camping with my family and some family friends at a beach house in Waialua. While racking my brain to come up with an idea for a physics blog, I recalled a hike we went on above Dillingham Airfield. The path itself was pretty steep and it made for a moderately challenging hike, but I can now look back on it with the greater understanding afforded by PHYSICS! Here is a picture taken by one of my friends during the hike:

If I were to draw a free body diagram of myself in this picture (pretending that I'm not pushing off of the earth, thereby increasing the normal force), it would have these elements:
- An incline of maybe 50 degrees
- Weight vector straight down of 9.8m (m being my mass)
- Normal force perpendicular to the incline of 9.8mcos50
- Friction equal to the normal force times the coefficient of STATIC friction (I'm not sliding)

In reality, there would be a push force from my steps but we don't really know how to implement that because it would increase the normal force; however, the push would have to offset the x-component of the weight vector and the friction in order for me to move at a constant velocity.

Enjoying nature is even more fun with a deeper understanding of physics!! :)