2007-10-18 -
Today's nonsense
- Homework due. pg. 105 #18,20-29,31
- You will be working on a lab writeup tomorrow while Spiller is sick. He's going to get blood taken, which takes, what, he gets there early, so he'll be out by 8:15, and he doesn't want to drive or pass out and hit his head, so he's not going anywhere. Phoebe understands. Mrs. Spiller is subbing- it keeps the money in the family.
- Need to start keeping track of time that is spent slacking off.
"At Wall-Mart, for a dollar, they have these, this is for the Halloween thing, they were like the collapsable pumpkins, which had wires in them for storage and all, and they had a little basket, should Math Club get some of them as prizes? I don't know because we'd have to buy enough for everybody if we were to get enough for everybody and we don't know how many there are. At the last Bingo game we could say "Okay now we're playing for all of the Halloween stuff." No, they're like pumpkins but a basket that's collapsable, so it springs up so that you can collapse it, it's like a dollar each. I'm curious, I want to hear what Luisa has to say. No, it just has a little face like it was a jackolantern. Hand-sewn quilt, Mrs. Gilson and the quilting guild .... Are we ready? Are we waiting for the toaster? I have to have my keys. This whole NHS thing and them just changing days ... I mean, we could do Wednesday, what's Wednesday mornings, meetings, and then if we have a faculty meeting we will not have one that week. I'm surprised calculus two hasn't griped about this. Physics 2, and then the degree symbol, it's very creative, you just don't get it. ... If you're going to refuse to wear the ID when you have it, we should just write you up. If they didn't give us such cheap IDs, maybe we would wear it. I've had the same ID for ... so you have another one that is broken? Do you have another one? Is it broken? May I see it? If this is an angle, then what is this? "
A WRECKED ANGLE
Imagine a spring sitting there doing nothing. But what if we stretched it or compressed it? The amount of force required to compress it, well, each spring has a certain constant that applies to it.
Hooke's law
When a spring is compressed or extended by a small amount, delta x, the force required to do so is proportional to "delta x":
F_x = -k(delta x) where k is the unique force constant
The value k is different for each spring.
ex 1) A 110 kg baseball player hangs on the rim following a dunk, when he comes to rest, the rim is bent down 15 cm. Assume the rim has spring-like behavior.and claculate its force constant, k.
"So they wiped out all of those stores? The movie place by the gas station? They took down all of that. It's supposed to be a CVS. Aren't we getting one in Buda too? No, Walgreens. Somebody keeps talking about a Supertarget coming into Kyle, by Home Depot, and an HEB Plus? This is a big time. It's called competition. And we're going to have a hospital. We should ask Alex, his father is an economic developer. You may begin!"
He's just hanging there on the rim. So we know that 110 kg is his mass. And of course, gravity we're going with 9.81 m/sec^2. So his weight comes out to be 1079.1 Newtons. So that's the force that's coming over here. So Weight = 1079.1 N. What are the units on k? Force does not equal distance. This is kind of like with the gas constant in chemistry. It has to have units to make the equation come out all the same. Newton is a kg * m per sec^2.
Quite often when we are talking about force, we're talking about the magnitude, so to say the positivity/negativity of the force means that you're just looking at the direction as well.
Let's talk about that monkey that we were talking about a few days ago. The monkey and that bananna.
2) A 4 kg bunch of bannananas is suspended motionless. from a spring balance whose force constant is k = 300 N/m. By how much is the srping stretched?
Tomorrow we will do lab writeups. There will be no particular style that is mandated, but particular things need to be included. This will be the "one free ride" lab writeup.
What are we doing with this data? Now, every time you do a problem with objects falling in the air, we always say to neglect air resistance, the idea with the coffee filters is that they will reach terminal velocity very quickly, so one coffee filter versus four, which one will hit terminal velocity first? The one. That's the kind of thing that you will point out in your final conclusions in your lab, or things that you could do differentfly if you were to do it again, the brilliant idea of doing the four first and then taking one out, that's a really good idea, but Dakota's group found that doing them from 1 to 4 is kind of bad, so ...
You don't need to write this down, it will be on the handout: mass * acceleration = mass * acceleration due to gravity if there is no wind resistance. Obviously, and this is given on the paper, you don't need to write this, unless there's a drag force, which would mean that m * a = m * g - F_drag. This drag force is F_drag = bv^n. Do you know what the b stands for? The b value is a velocity.
When you drop something, it gets faster and faster theoretically, but if you were to drop a feather or coffee filter, it did not get faster and faster, it got faster at first, and then it just floated down because it hit terminal velocity, because of air resistance. So the terminal velocity is dependent on the shape of the filter etc. So hopefully all of the filters were the same shape and as we stretched them out they were not the same. Our goal is to find the "N" value.