shoes and carpets

Well, I've never actually gotten shocked at home from static electricity, but I remember all the times it happened in Las Vegas. Pretty much from the time I walked into the hotel I started getting shocked every time I touched someone else or a door knob. I drag my feet a lot so I must have been picking up a lot of electrons from the carpet that wanted to be released because the body naturally wants to be neutral, not charged. Besides dragging my feet, the weather conditions over there probably helped build the static electricity to levels higher than they are in Hawaii. The humidity over here must allow the electrons to leak off at a faster pace than in Vegas. I guess all I have to do is stay away from really dry or cold places.

leftovers...

Well, everyone was out at a Superbowl party and left me home to fend for myself so i ate leftovers. That's when I saw the saran wrap on the bowl and remembered static friction from the last test. When rolling the wrap out of the container, electrons are pulled from the level below and the top layer is positive, which is why it sticks so well to itself. This is because the posititve charged side and the negative charged sides are attracted to each other. And especially because the refrigerator is so cold, the saran wrap must stick to it better (because the physics room needed to be colder for the lab to work better). Then, when I crumpled it up and threw the saran wrap into the trash, it didn't stick to itself because the electrons from the negative side transferred to the positive side so it was no longer polar.

car shock

As I was getting out of the car today, I got shocked again. The feeling is just like the zap from Vegas when you accidentally bump into someone. When two objects touch, if one has a charge and the other is neutral, electrons will move to whichever object is more positive. This is because objects want to stay neutral. In the situation with my car, I'm pretty sure that I'm neutral and the car door must have a negative charge. I'm probably neutral because I don't remember doing anything that would cause me to gain or lose electrons. The rubber on the car door might have gotten some electrons from the metal part of the car when I opened the door, giving it a negative charge. (The rubber is an insulator so electrons would not flow throughout all of it.) The electrons passed from the door to my hand, which is why I think that the zap occured. (But it's weird how my car only seems to shock me, not anyone else that rides in it.)

Flying Fish...

This was from Winter Break, and the story behind it has quite a bit of physics involved. Me and my friend were fishing on the Big Island and she caught the first fish. Since the fish wanted to get away with the bait, it tried to swim away. This caused tension in the fishing line (considering it was only a bamboo pole). However, the force with which she pulled the pole was great enough to allow it to overcome rotational inertia and begin rotating (clockwise in this picture). This also made the fish, still attached to the bait, go in a circular motion (just like the ball and string exercise in class). However, it couldn't hold on long enough, and ended up flying in a tangent and back into the water on the other side of the rocks. In the end, she lost a tasty snack, but she gained an understanding of tension, rotational inertia, and tangential vectors.

Bridge Balance

I found an example of torque just in time for the upcoming test. The bridge is really old and falling apart, but its weight is still being held up by the normal force of the ground on both sides. The weight is focused in the CM (center of mass), which probably isn't in the middle of the bridge since parts of the fence have already fallen off. The weight has to be supported by the ground, because otherwise the it would keep on falling. Besides the forces cancelling each other out, no matter where the fulcrum is, the torque exerted by the forces also have to cancel each other because otherwise the bridge would be rotating instead of standing still. (Torque is equal to forcexdistance from the fulcrum). The balance for the forces and torque exerted are the reason why this bridge stays still.

torque

Like the example in my homework, I chose to talk about a light switch for this journal. While the light switch cannot do a complete rotation, it does go in half of a rotation when torque is exerted on it. To turn the lights on, the force exerted is positive, and thus it has positive torque. To turn the lights off, negative torque has to be exerted. The lever arm is the distance between the switch attached to the wall and the point where the finger hits it. As we learned, the greater the distance, the less force needed to flip the switch. This is why it would make more sense to flip the switch at its tip rather than the point closest to the wall. (Although it takes relatively little force to begin with, hitting the switch at the tip makes the task even easier to do!)

tests and washing machines

After the test, I kept thinking about that problem with the washing machine so I took a good look at the one I have at home. In a sense, the physics behind a washing machine is the same for that gravitron ride. The clothes push against the side of the machine, which results in a normal force pointing towards the middle. This normal force is also the centripetal force in the spinning action (and is equal to mass x centripetal acceleration). The holes on the side are for the water to leave at a tangent (because the water does not have enough force to keep it going in a circular motion). Also, because the motion is horizontal and not vertical, the centripetal force does not change throughout the motion. After seeing the real thing, answering the question seems a lot easier.