physics journal #8

this weekend i experienced the centripetal acceleration. I was inside a car with my friend and we made a turn on one of the intersection. As we turned the corner, i thought about the ideas of centripetal acceleration and started explaining it to my friend. I told him that because we were going at 40 mph on the straight and made a turn with a constant velocity, and with the radius of the intersection curve being about 10m or so, we can calculate the centripetal acceleration. i simply converted 40mph into kmph, which is 40mph*1.6km/mile = 64km/h. Now i could apply that velocity-squared/radius equation and solved for the acceleration, which was approximately 409.6km/hr^2. when i told this fact to my friend who was driving, he was impressed in how fast we were accelerating towards center as we turned. I also explained to him about how important free-body diagram was when dealing with inclined plane problems. Because regular physics students are studying work and energy right now, i was helping him out by teaching what i learned in ap physics. That is, as i said, draw freebody diagram.

Physics Journal #7

This weekend we went to Hawaiian Bryans and played pool. There were many things i could relate to physics in pool. As a matter of fact, i became better at pool (i think) because of physics. Because we learned that the direction of the target ball after the collision is proportional to the direction of the line that connects centers of cueball's and the target ball's masses, i was able to put in more balls than before because i had better idea of where the ball will go. However, due to friction, spin of the ball, and other extraneous factors, the ball didnt go the way i expected to go all the time. Also, the cue ball didnt always go perpendicular to the direction of the target ball went after the collision. that is probably because the mass of the cue ball is a little greater than the mass of the target ball. Another factor that made the error is probably spin. Because we didnt learn spin of the ball yet, we cant really analyze how that could affect the direction of the ball.
I was also aware of friction force between table and the ball. Without it, the ball would go all over the place without stopping. It would be interesting but it would be stupid to play because you can do nothing other than wait for the balls to go in the pocket.

Physics journal #6

At senior camp, we played this high calibur table game uniquely designed for the 21st century lifestyle. This game is called bulletball, and the objective of the game is to get the ball (or some kind of object) past your opponent by utilizing your forearm and/or hand. We played 6-man bulletball with water bottle that was provided at the camp. As we hit the bottle back and forth the table, i remembered that i could use my physics knowledge to analyze how this works in physics. As we hit the ball, we are using momentum and impulse. Momentum of an object is greater if the mass is greater and since the bottle we used were much greater than a ping pong ball that we normally use, the momentum was much greater. Also, just like the lab we did, as the bottle came to me, i thought to myself, if i hit the bottle to the other side and assume that velocity is positive, then the velocity of the bottle coming near me is negative. Therefore, if i apply a great force in that, i could hit the ball so much faster to my opponent. So i did apply a lot of force so i could hit the bottle with great velocity and get it past my opponents.

Physics Journal #5

This weekend, we had our xc meet at kamehameha school. Because of the rain, the ground was insanely muddy and it made us have hard time running the race. Because of the slipperliness, one of our runner fell down right after the race began. When the officials stopped the race because of an unadvantageous start, my friend and i discussed about how this has something to do with physics. We both agreed that the ground has a low static friction coefficient. Because of that, as the force we put in to kick the ground increases, there's higher chance of our shoes slipping on the ground. We discussed on what the best way to deal with this problem. One of my friend said it would be better to run from heel to toe because there would be more surface for the shoe to grip on the ground. However, i disagreed with that because i thought the longer time we have our foot on the ground would increase the chance of our foot slipping. Therefore, i suggested to run on the toes and kicking the ground more perpendicular to the ground than we usually do because if we kick the ground almost perpendicular to the ground, the friction force would be at its max. However, if you ran from heal to toe, it would be difficult to do that because you must exert a force in a backward direction which would lower the normal force which would lower the friction force, making the shoes slip on the ground.

Physics Journal #4: Work

Work is network times displacement of an object due to the force. this week, we had track workouts for our cross country. I ran 800m interval 8 times, so I ran 6400m (8x800=6400, which is equavalent to running running 4 miles) but my displacement is 0m (because I ran around track which means I ran back to where i started 16 times in total). In physics, our whole workout that we put so much effort on requires no work since the final displacement is 0m. It's a little bit disappointing because it feels like I'm wasting my time doing the same amount of work as not doing anything. Thinking like this made me feel like running on track is a bit retarded because you could just not run still have the same amount of work done from running around track, at least in physics definition. On top of that, it's not really me pushing myself, it's the earth that's pushing me.