Orchestra Concert

This is my brother with his violin because he had his orchestra concert this afternoon. While I was watching and listening to his orchestra concert, I thought again of physics, mainly the current concept of sound. My brother often rubs his bow with a block of rosin. I realized that this actually has a purpose! (No, I do not play the violin or any musical instrument for that matter...) The rosin creates friction between the bow and the strings on the violin so that the strings vibrate when the bow is pushed/ pulled over the strings. This vibration creates sound waves, oscillations in the air resulting from differences in pressure.

Before the concert actually started, the students had to tune their instruments. The teacher had to make sure that everyone's instruments were playing the same notes at the same frequencies, otherwise the audience would hear random weird noises throughout the concert...Each note has a specific frequency for a certain instrument, as we found in the lab with the super cool Casio keyboard (and our class totally did NOT press the demo button when doc left the room...right? :P). Also, the frequency of note doubles when it is played 1 octave higher, as higher notes have higher frequencies (1/T, cycles/s).

Rinsing Out a Bottle of Gatorade

While I was rinsing out a bottle of Gatorade to be recycled, I realized that the water flowing out of the bottle exhibited fluid continuity. I can apply the equation for continuity of fluids because the water is in a closed system until it leaves the bottle and water is similar to an ideal fluid because it is nearly incompressible. According to the equation A1v1=A2v2, the velocity of the water should be higher where the area is smaller. The neck of the bottle has a smaller area, so the water flows out faster than at the bottom of the bottle (top in the picture). However, after the water leaves the bottle, the equation of fluid continuity can no longer be applied. The water then falls in free-fall motion due to the (downward!) force of gravity. Sorry for the lame picture...it was very difficult to take a picture while the water was actually flowing out of the bottle...

Swimming (and other floating activities)

During this Thanksgiving weekend, I was relaxing and floating on my back in a swimming pool. But, physics soon invaded my thoughts and I started thinking about physics and Archimedes' principle. According to Archimedes' principle, the buoyant force keeping me afloat was equal to the weight of the water I displaced. I realized that I was able to float because the density of the pool water was greater than my density (m/v). The upward buoyant force was enough to counter the downward force of my weight. (Ok, so sorry I don't have any picture for this part.)

This is a picture of a cruise ship on the other side of Glacier Bay (Alaska) when I went on a cruise this past summer. Although the ship seems large and heavy, it floats because its density is less than the density of the water it is sitting in. All of these cruise ships could not possibly exist without buoyant forces!

Doors

My door, the gateway to the wonderful place where I get to do my endless amounts of homework and sleep every now and then...I realized that this door I use everyday demonstrates torque and rotational motion. When I turn the doorknob to open the door, my hand exerts a torque on the doorknob, causing it to move in a circular path. When I push the door open, the door is moving in a circular path with the axis of rotation going vertically through the two hinges. This circular motion is due to the torque I exerted on the door, which is equal to rFsintheta. Therefore, if the doorknob was closer to the axis of rotation, the radius would be shorter, so the door would be harder to open because the torque exerted on the door would be less even if I pushed on the door with the same amount of force. This idea is demonstrated at Forever 21 because the doors of the dressing rooms each have a huge doorknob right in the middle of the door. I found that these doorknobs are not very effective because in addition to the fact that they don't turn, it is harder to open the door when pushing on these huge doorknobs instead of just pushing on the edge of the door opposite of the hinges. Such impractical, physics-ignorant decorations...

Dance Concert

Yesterday, I went to the Castle High School Dance Concert. The contemporary dances were pretty cool. In many of the numbers, the dancers leaped as they moved across the stage. The motion as the dancers leaped and fell back to the floor is an example of projectile motion. In order to move across the stage instead of jumping in place, the dancers had to leap with a certain x-velocity. Also, another basic move that was repeated was turning. The dancers doing single and double turns showed rotational motion. Eventually, the dancers would stop turning after a turn or two because of the torques opposing the rotational motion. There was a torque of friction acting on the foot spinning on the floor and there was also a torque of air resistance on the dancer's body. The dancers had to put in enough initial angular velocity to create a large enough torque to overcome the opposing torques of friction and air resistance to complete the turns.

Fan

After I turned on my fan, I realized that the fan showed uniform circular motion because the blades moved in a circular path at a constant speed. The period of the blades in the fan (the time it takes for the blades to make 1 complete turn) is equal to 2πr/v. The centripetal force on the blades is equal to mvv/r and the centripetal acceleration is equal to vv/r. Because the air was too strong at first, I turned the knob on the side of the fan to reduce the fan speed. The blades slowed down, so the speed was not constant anymore and the motion became just regular rotational motion. This essentially reduced the angular acceleration of the blades, which would be equal to change in angular velocity/ change in time. Well, I guess I can't ever run away from physics...it's everywhere...can't even turn on my fan without thinking about physics concepts and equations...

Reducing the Impulse of a Juice Can

The other day, my friend tossed me a can of juice. Before I could mention that throwing the can was not the best idea considering my slightly incompetent catching skills, she threw the can towards me in a projectile motion. In order to prevent any injury to myself, I caught the can before it hit me and cradled it towards my body. Since J=force*time, cradling the can increased the time of the impulse, and therefore decreased the force felt by my hand to stop the can. If I had held out my hands stiffly or caught the can after it hit my body, I would have felt a stronger force upon impact (ouch). If I knew the mass of the can, speed of the can before it hit my hand, and the time of the impulse, I could calculate the force I felt using the equation J=change in p=force*time. I realized that this situation was similar to the egg catching game because both involved cradling an object to reduce the force of impulse.

How UH scored the 1st 2 points...Physics Incompetence!

Yesterday, I went to watch the UH vs. Boise State football game. Not that I'm a huge UH football fan or someone who actually understands the game of football, but I did witness some awesome physics in action! So for people who didn't watch the game, UH finally scored the 1st 2 points in the 3rd quarter due to a safety or something (still not completely sure what that means). Anyways, the Boise State center snapped the ball to their quarterback, but because the angle of the initial velocity with the ground was too high, the ball flew over the quarterback's head. Next, a UH player tried to catch the ball, but because his hands were held out stiffly, the time of impact with the ball and his hands was reduced. Therefore, the force needed to stop the ball increased because of the impulse=F*elapsed time equation. The increase in force needed to stop the ball caused the ball to bounce out of the UH player's stiff hands. Since the UH player couldn't catch the ball, he tackled the Boise State player, and UH got 2 points for the safety! (Sorry if this is inaccurate because I don't completely understand the game of football...)

The Last 100m Sprint (supposedly)-XC

This is a picture of me approaching the finish line at the Kamehameha Invitational last Saturday. After learning about momentum and impulse this week, I realized that these concepts closely tie into the finish of a cross-country race. My understanding of momentum and impulse from physics has helped me to understand why my coach tells everyone to run THROUGH the finish line (as opposed to stopping at the finish line). Impulse is equal to the change in momentum and the average force*elapsed time. Momentum is mass*velocity, so the change in my momentum at the finish is equal to -my mass*my sprinting speed because if I stop completely at the end my final velocity is 0. The value for change in momentum should be equal to average force*elapsed time, since both expressions are equivalent to impulse. Because the change in momentum is not 0, the equation requires that the elapsed time cannot be zero either. Therefore, since I am changing my momentum at the finish line, I must take time to slow down to rest; I cannot stop instantaneously. Because I have to slow down over a period of time to make the change in momentum, I would have to start decreasing my speed before the finish line in order to stop at the finish line. This would mean that I cannot run at sprinting speed for the whole 100m stretch, hence a slower time and getting passed by other runners right at the finish line. By following the coach's advice and running THROUGH the finish line, I will start reducing my speed after I cross the finish line, so I will be able to run the entire last 100m at top speed (and hopefully pass other runners who aren't thinking about the physics behind their race finish).

Physics Toy

I came across this toy and totally thought of the wonderful world of Physics! When you push down one of the dolphins and then let go, the dolphins on each side move towards the ball in a circular path alternatively. First of all, because of the low friction between the metal parts, the dolphins will continue to move for quite some time after one of the dolphins was first pushed down. This exhibits Newton's first law of motion because the dolphins continue to move until the force of friction eventually acts on the system. This dolphin toy also shows the idea of conservation of total mechanical energy. When one pair of dolphins is pulled up a certain distance and held at rest, the kinetic energy is 0 and the potential energy is mgh. The total mechanical energy of the pair of dolphins just before they change direction is the same as the total mechanical energy in the beginning, except in the end the potential energy is 0 and the kinetic energy is mgh. The forces acting on the system include a magnetic force from a magnet inside the blue base (pulling the dolphin downwards), gravity (which is always, always, always pulling down towards the center of the earth, and tension.

A Shower of Projectile Motion

I decided to take a break and shower after many hours of studying. Even though I tried to avoid thinking, a few physics concepts hit me on the head (quite literally actually). I realized that the stream of water coming out from the shower head exhibited projectile motion. Since the direction of the initial horizontal velocity was parallel to the ground and there was no initial vertical velocity, the equations in the picture represent the distance from the shower head to the ground and the horizontal distance from the shower head in which the stream of water lands. Since we learned in the projectile labs (the ones with the monkeys and bananas) that vertical and horizontal motion are independent, I know that when I adjusted the strength of the water stream, I was only changing the initial horizontal velocity (and therefore the horizontal displacement), not the time it takes for the stream of water to travel from the shower head to the ground. It's amazing how physics is everywhere in the world around us. We can never escape the laws of physics!

Hanging Chandelier

As I was eating dinner in the kitchen, I noticed the chandelier hanging from the ceiling. I was reminded of the free body diagrams that we drew in physics for similar hanging objects. The free body diagram for the chandelier is shown in the picture, if the mass of the chain could be 0. The only two forces acting on the chandelier is weight, the mass of the chandelier*the acceleration of gravity (9.8 m/s*s), and tension. Weight is directed downwards towards the center of the earth as it always, always, always is. Because the system has no acceleration, the net force is also 0 according to the F=ma (F=net force) equation associated w/ Newton's second law. In order for the net force to be 0, the magnitudes of mg and T must be equal. This observation also relates to Newton's third law because mg and T create a force pair, being that the two forces are equal in magnitude, but opposite in direction. These forces with equal magnitudes and opposite direction allow the chandelier to hang from the ceiling rather than crash to the ground or the ceiling.

First Post...

Wow, I can't believed I've already survived like a month of this AP Physics class. This class has been pretty challenging for me, as I imagined it would be. I'm slowly learning that this independent learning process requires keeping up with work daily, whether it be homework or labs. I have also realized that physics involves a different kind of learning from either chemistry or biology. It is important to thoroughly understand concepts in addition to memorizing and applying specific equations. As indicated by the picture, I'm a confused little penguin in this class most of the time, trying to make sense of everything I'm learning. I hope that as the year goes on I will be able to understand things better. Labs and problem sets can be especially difficult, but I find that they are easier to understand after discussing them with my classmates and/ or doc. The tests are pretty hard and I can't imagine finishing them in 1 period yet, but I seem to understand things a lot better after going over the tests. I'm excited to learn more concepts and hopefully I will continue to adjust to the fast pace of this class. I know that this class is only going to get harder, but I'm ready to keep up with the challenge.