Tuesday, March 22, 2011

March 22nd, 2011 - Seasons and Sunlight

Today in class, the first thing that we did in class was discuss why we have seasons. We hypothesized that seasons occur because of the Earth tilting different directions and the Earth's position in orbit. Later we learned that the Earth's tilt is always in the same direction and is
constant. The Earth's tilt is always 23.6 degrees if you draw a line from each of the poles.

Next, we discussed direct and indirect sunlight. We already know that the Earth's position around the sun changes making the Earth point either away or towards the sun. The hemisphere tilted towards the sunlight will receive direct sunlight, and the other will receive indirect sunlight. The amount of direct sunlight on the Earth was displayed in
our simulation we did yesterday in the bottom chart with the yellow dot being either spread or focused.

Next, Mr. F had us do an experiment to prove this. Mr. F has a device that measured the amount of solar energy in a room. Then Brady climbed on top of desk and took a solar energy source (a light) and shone it over the device. As Mr. Finley slowly moved the device upwards, the solar energy decreased 0.1. This proves that direct and indirect sunlight is true.
Therefore, seasons occur because of the position the Earth is around the sun. When the Northern hemisphere is receiving indirect sunlight, it is winter while it is summer in the Southern hemisphere. When the Northern hemisphere is receiving direct sunlight, it is summer while it is winter in the Southern hemisphere.

- J. L. (4th blog)

Monday, March 14, 2011

3/14 Phet Simulation

Tomorrow there will be a quiz so today is a review.

SD pushed MM on a cart towards the wall and he only moved a few feet and slowly. The harder she pushes, the further MM goes and the faster he gets there. The greater the force the faster the acceleration. The more mass of the object the slower the acceleration. The less smooth the surface the greater the friction, the slower the acceleration. And finally, unbalanced force accelerates while a balanced force goes at a constant rate. Today we'll test all these hypothesises by using Phet.


We tested it by having a little man push a box across a friction-less surface (ice). The harder he pushed, the faster and further the box went. This proves our hypothesis.

Then, the man pushed the box and the refrigerator both with 900 N on ice. The box was moving traveled across the screen in about 3 seconds while it took the refrigerator 5 seconds. This proves our hypothesis that greater masses slow down the acceleration.

The man pushed the box much faster on a friction-less surface (ice) versus wood and the box accelerated faster. We made sure the box was moving at a constant rate of 500 N. This proves our hypothesis.

We will test by pushing a box across the friction-less ice to see if we push it once, how much it accelerates. If there is a balanced force of 0 mph, the box goes at a constant rate. This was proved by us not pushing/touching the box.

This is a picture of the little man pushing the box on a wodden surface with unbalanced forces of 777 N.



JF (4th blog)

Saturday, March 12, 2011

Hi everyone!
Today is March 11, 2011

The first thing we did today was go over the homework.
We added in arrows to the dot diagram in between the dot because we realized that regular dot diagrams are way too primitive. The arrows show direction, and speed (the longer it is, the faster it goes)

Here is a description of the dot diagrams
A) The dots get further apart as they go up. The arrows point up
B) The arrows get closer together as they go up. The arrows are pointing up.
C) There is just one dot
D) The dots get further apart as they go down. The arrows point down
E) The arrows get closer together as they go down. The arrows point down.

The second, third, and fifth one we had questions about

In B:
The ball leaves your hand moving rather fast, but it slows down. This is made very clear by the ball stopping and hovering at the top of its ascent .

In C:There is only one dot in the diagram because at the top of its path, the ball stops and hovers for a very short time. This means it is not moving, and therefore there is only one dot.

In E:There was also a question about E. We wondered why, if you stop it when you catch it, it says it is still going down. Mr. Finley showed us an example. When he caught the object, his arms went down to compensate for the mass of it.

Here is a video showing what would happen in this experiment. It will help explain the things discussed
above.
http://paer.rutgers.edu/pt3/movies/throw.mov

Then Mr.Finley showed us an example. He pushed a dictionary across the table. The book left his hand, then moved across the table, slowied down, and finally stopped
Then we made a force diagram, and explain why this happens.

My group said that Mr. Finley exerted a horizontal force, but once it left his hand,
only the Earth and the table was pulling on it. Then we went over it.

Another group said friction was doing force.

Another idea was that there was unbalanced force being exerted by the surface of the table. In other words, it was pushing back. DB asked if the table could push up and back. We determined that it can. The surface of the table was pushing back, and the whole table was pushing up. This is the solution we went with.

ADVICE:Remember that friction is just like heat. It is NOT a physical object. Juts like you cant add heat, friction can't do force. Only tangible objects can exert force on a system. This is very important to remember, and can be a little bit confusing.

MK(Fourth Post)

Monday, March 7, 2011

March 7th, 2011

Today when we walked into class, we got right to the questions from Friday. We took out our homework from the 3rd, and JF and AL drew the force diagrams on the boards from the picture frame and the car problems.



AL had labeled her force diagram like this (on the top) force exerted from the Earth on Car, then the dot was labeled car, and on the bottom it was the force exerted from the road to on the car. But she had mixed the two up, the force from the Earth was on the bottom, and the road on the top, so JP fixed them.

JF had labeled hers as so; on the top, it was the force from the string and the middle was the picture with the frame and the bottom was the force on the earth

The arrows on the picture frame was very short because the picture frame isn't exerting as much force as the car.



Then Finley showed us a "video" on PHET that was a man pushing a box on the ice and we had to make a force diagram on the "video"

EC and I said that if force is exerted on the box, then the box is going to continue traveling for awhile, but before the earth's force is going to slow the box down.


JG (Fourth Time)

Thursday, March 3, 2011

3/3/2011 Period 2

The main thing we did today was go over the HW, but there were a lot of very important questions that came up. Our HW had 2 questions that each had a, b, and c.

Question 1 had a scenario about a jacket on a hook.
A said: what are the objects with which the jacket interacts? What object is our system?
When we discussed this in class we came up with the jacket touching the hook, and that the jacket was the point of interest and the system.

B said: Represent the situation with a force diagram.
The force diagram looked a little like this. The hook was pushing the jacket up, and the earth was pulling the jacket down. The arrows have to be equal because if the hook exerted more force than the earth the jacket would keep rising, if the earth was exerting more force than it would pull the jacket down to the ground.




Hook
+70N


Jacket
0N

Earth
-70N




Alexia had a great comment about the hook, she thought that the hook wasn't exerting any force. That's when we had a class discussion and found out that if the hook wasn't exerting any force than the jacket would just fall because there is nothing holding it up..

C said: How would the force diagram change if you put a heavy book in your pocket.
If you put a book in your pocket than the diagram would look more like this. The earth would be exerting more force downward and the hook would be exerting more force upward. The jacket would still be in the same spot because the forces are still equal.




Hook
+100N

Jacket
0N


Earth
-100N


Question 2 was about 2 people carrying a suitcase.

You had to make a # sentence and a force diagram for A. The # sentence i used was +20 + -20 = 0, and this was my force diagram.




People
+20
Suitcase
0N
Earth
-20N
For B you needed to put the total force exerted on the suitcase. That would be again O because 20+(-20) is 0.

C asked how you decided which side you decided was to be positive and which negative. The positive side goes up because the positive side is always represented by going up or right and the negative side is always represented by left or down.

We didn't do anything else in class to today, but we do have 4 Q's for HW.

JB Post #3

Wednesday, March 2, 2011

New Unit - Astronomy

Today we are starting a new unit - Astronomy


We started off class with a demonstration of holding a bowling ball in one hand and a ping pong ball in the other. Then we observed what happened.

  • You have to push up to hold each ball

  • There is a different push on both sides because of the weight difference



We then discussed a new term, force, and that you are applying force to the ball to hold it.
Force - Interaction between 2 or more objects. (push, pull, etc.)




Next, we talked about what the previous class had said about this demonstration.

"The student had to have done work to the ball in order to hold it up." This is not true because you are applying force to the ball, not work. The ball has gravitational potential energy when it's being held, but nothing is doing work to it.



QuEsTiOnS

+What would happen is this was the only force exerting the bowling ball?

-The only force is pushing up, so it would keep going up and not come down



+Are there any other objects exerting a force?

-The earth is pushing the ball down.





There is an equal amount of force on both sides so it is balanced.
Our number statement for this scenario would be: +7 + -7 = 0



This is because you are giving the ball energy when you hold it above the ground. The earth is pushing down on the ball, making it lose its energy.

During class today, someone mentioned something about the displacement of the ball. I didn't really understand that and why it was displacement. Could anyone tell me about it?

EE (3rd blog)