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.

waikiki

I was at waikiki this weekend and as I was taking pictures of people walking on the street I noticed that the image of the cars looked really interesting. It's kind of dark so only the lights are really noticeable. Since the cars were in motion, they had kinetic energy (.5mvsquared), and since they were probably accelerating (change in velocity or direction), they also had work (change in kinetic energy) and power (change in work over time). The motor in the car is doing the work to make the car accelerate and gain kinetic energy. Even a simple thing like a car driving involves the majority of the lessons we have learned so far. If there was a collision (although I wouldn't hope to see one) then that would have involved the latest chapter we covered. I seem to notice physics in places where there are cars...

trash cans and newton

I was in Moanalua Gardens today and as I was walking in I noticed a trash canbeing held up by rocks. I don't really know why it needed rocks to support it, but I do know that there is some physics involved. The weight (massxgravity) of the trashcan and the rocks is being balanced by the normal force of the ground. The weight of the trashcan is also pushing against the rocks, which are also pushing it back because for every force there is an equal and opposite one. The forces are balanced because the trashcan and rocks are at rest. There is also only vertical forces acting upon the trashcan and rocks. Although it is strange to have a trashcan sitting on rocks, at least there's some physics involved!

Tension in the air

My mom just bought some poupouri for her car and as I was filling the little pouch with all of the beads, I was reminded of tension. As I was tugging the pouch shut, I was exerting a force on the string that added to the tension in it. The combined vertical tension of the two strings was equal to the weight (massxgravity) of the pouch and the horizontal tension of the strings going in opposite directions were equal to each other once the pouch was pulled shut. However, while I was pulling the strings, the left side seemed longer than the right side, which I think means that I pulled with more force with my left hand than my right. But then, time is used for power, so maybe my left hand used more power?

self/course eval.

To be honest, I still feel a bit apprehensive about the course. It's still the most interesting science class that I've had so far because of all the labs. They always involve quite a bit of work, but at least the concepts are easier to understand. However, there is still a little bit of confusion here and there regarding certain concepts (like Work) that make me worried that the concepts will only get harder in the future. My goal in this class would be to get the A. So far, I've turned in all my work on time and have been trying to understand the concepts well so I think I have put out quite a bit of effort.

Ramen...

Today we all went driving around Kailua and stopped over at this place to eat ramen. While waiting for our order, I noticed that there were a bunch of lanterns and decorations hanging all over the place and figured they might have something to do with the things that we learned about forces. Since the hangings were at rest (due to the lack of wind outside and inside the restaurant), the basic forces on the hangings were their weight and the normal forces holding them up to the ceiling. Since the heart hanging inside was at rest, the net force must be 0N. This would mean that the weight of it (its mass x gravity) must be equal to its normal force. This is from Newton's first and second laws, for an object at rest must have a net force of 0N and for every force, there must be an equal and opposite force.

going nowhere...

I thought this parked car was a good example of what we're learning right now. Gravity is pulling it down and normal force from the ground is pulling it up. Because of its weight (mass x gravity) and the equivalent normal force, the car is going nowhere vertically. There are also no forces pushing it in any other direction so because of this, its' net force is 0. This is the reason why it's still at rest. Newton's first law says that unless acted upon by a force, things that are at rest stay at rest and things that are in motion stay in motion. This car won't move/go anywhere until its net force changes from 0 to some other number. (Since I don't think anyone's going to try and push this car, starting the engine is probably the only way it's going to go anywhere!)

dents

i was looking at all of the dents on my neighbor's car when it hit me (not literally) that the cause of them had something to do with physics. There's a tree high above where he parks so the nuts fall down and leave the dents. I guess it's something similar to free fall because excluding the wind and air resistance, the nuts are being pulled down by gravity so their vertical velocity is negatively accelerating. It's the same concept as my cat falling off the lanai although I think air resistance has a bigger effect on the nuts because although they are pretty heavy, they aren't as heavy as a cat. The top of the tree is around the same height as my lanai so ignoring air resistance, the nuts probably fall at around -20.288 m/s as well (after using the kinematic equation again). Although if you do consider air resistance, they probably fall at a slower rate than that because they'd get more air resistance than my cat. There sure seems to be a lot of falling around here...

raining cats

I was thinking about what I could do for this journal when I remembered how one of my cats had jumped off the lanai awhile ago. He was trying to catch a bird and although he did get it, he also fell about 21 meters down. He fell straight down so if air resistance is ignored, his acceleration would be -9.8m/s^2. If he started with 0m/s vertical velocity, that would mean his final vertical velocity would be around -20.288m/s. (I found this out with the kinematic equation V^2=InitialV^2 +2ax.) He hit the bush, and considering the rate at which he fell, that was probably way better than him hitting the ground. (His displacement was -21m because he fell down to a lower position than where he started, his acceleration was -9.8m/s^2 because of gravity and the fact that he was speeding up in the negative direction, and his velocity was -20.288m/s because he was going in the negative direction.) He had a major run in with physics, but he survived!

so far...

http://www.mulimed.com/images/Worry.gif

So far this class seems manageable, but only time will tell...It does however seem to have better labs than biology or chemistry. The labs take some time to do, but they're fun. I'm interested to find out what all of the other labs will be about, but at the same time I'm still pretty worried about all the tests (like the one next week!). I'm also kind of worried about how difficult it will be to understand the concepts as the year goes by. I guess I'd have to say that I'm still a little apprehensive about the course....

darts

I was at a party this weekend and while me and my friends were playing darts I realized it had something to do with physics. It's the same concept I talked about last week, just applied to a different event. By throwing it, the dart gains velocity going from 0m/s to a velocity in a negative direction (left, according to the picture). This would also be considered acceleration because there is a change in velocity even though there isn't much of a change regarding direction. Because the distance between the board and the person is too close, the final velocity of the dart right when it hits the board is not 0m/s . However, it is positive acceleration because the dart's speed is slowing down over time and it is going in the negative direction.

Well, I just finished eating breakfast on the lanai and decided this picture would be a pretty good example of what we just learned in class. It's kind of small, but there's a car (which i'll call carA) trying to get onto the freeway in the top right corner. We learned in class that acceleration is the rate of change in velocity and/or direction. This change is going to be important for carA because while it doesn't have to change the general direction that it is going in, it does have to go at a faster velocity in order to reach the velocity of the other cars on the freeway. (if it maintained its velocity, it would be slower than the other cars and would probably wait forever before it could change lanes) If left is the negative direction and right is the positive direction, then carA would have negative acceleration because it's increasing its velocity in the negative direction. It would also have negative velocity because it's moving in the negative direction.