#12

This weekend was pretty awesome since it was four day weekend and there was barely any homework. It was pretty nice getting rest from everything once in a while. Therefore, i didnt really have anything physics related this weekend cuz i pretty much spent all my day at home just sitting around, doing nothing. But on saturday, i went out with my friends again to bryans (doc, you gotta come with us!). But since i already talked about physics of pool, im not going to. I actually want to talk about centripetal force and centrifugal force. while we were driving around, people in regular physics didnt know the difference between centrifugal and centripetal force. some of them even argued theyre the same thing. So i told them that centripetal force is the net force and centrifugal is the imaginary force that you feel. When we got to the curve, i told them there is radially inward acceleration and they nodded. And when everyone started to feel the push towards outside, i yelled "THIS IS CENTRIFUGAL FORCE!"
that was fun

#11

This weekend, i watched couple tv shows that dealt with water. One of them was mythbusters and what they were trying to do was to examine if all those ninja skills were actually possible in real life. They tried walking on water by using wooden panels. The point of that is to increase the volume and area of the object touching water proportional to the mass so it would have higher FB's. It sounds very reasonable and it sounds like it works using the wooden slippers because woods has not that much of a mass but can provide a good volume. However, the plan totally failed because the mass of a human being was too much for that FB created by wooden panels. Perhaps if it had a greater volume then maybe it could work out. So they used styrofoam and made a big shoes out of it. The volume of that shoes was apporoximately .9m cubed or something close to it. Im not sure the exact value but from my estimate, thats the volume. So the guy had totaly of 1.8m cubed as a volume for 2 shoes. And the plan was a success because the volume provided more FB force than the weight.

Physics Journal #10

Today, as i was watching the show Man vs Wild, the idea of using sun as a way to know the direction came across quite often. As i was watching and listening to the logic of that, i remembered that although it looks like sun is moving, its actually the earth that is rotating around the sun. Also, i remembered that earth rotates on its axis once every 24 hours. All of these informations reminded me of the lab we did. As i remembered the lab, i remembered that because theres a satellite in the outer space orbitting around at the same speed as the earth rotates.
Also, in man vs wild, there was a part when he slipped down the ice to move through the places to walk. The friction coefficient must have been very low (both static and kinetic) because he slipped down easily and quickly. I even thought that if we tried to find the speed he was sliding down, we could have just ommitted the friction force/work out of the system. Since i doubt the acceleration was constant, i would choose to use cons. of energy concept to find out his velocity, if i ever do.

Physics Journal #9

this weekend, we xc runners and supporters went to maui to compete in states championship. As a team we ran through the course and coaches made checkpoints about how to attack the course. While we were going through that, one thing caught my attention. When our coach told us to let the gravity do the work goin down the hill, i thought to myself, hey we learned this in physics. So with an intelligent mind of mine (yes you can laugh, doc), i yelled out, "guys, use the mg sin theta!" people in physics understood and laughed and people who didnt take physics needed an explanation so we all explained to the freshmen what we were referring to. we explained to them that the weight is mg and because it was an inclined plane, the net force is going downward parallelly along the surface of the inclined plane. therefore we use the mg sin(theta). Which means, on the other hand, when the runners were running upward, they were fighting back the force, mg sin (theta). Though it is one of the simplest physics we learned so far, it was good to review these kind of stuff.

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.