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)