Friday- January 11,2008- Day 81
On Friday, we started class reviewing Thursdays key message. The key message was the work-energy relationship. Work=force times distance=change in total energy. The equation is on your reference tables. Et=KE+PE+Q, then W=change in PE+change in KE+change in Q. The change in Q=Heat added to the system (work done against friction is lost as heat).
Next, we did a problem workshop consisting of groups of three maximum. These groups reviewed problems from worksheet number five, which was using solutions as a guide. This carried on for about fifteen minutes as Mr. Wirth went around and answered all the questions people had.ANother activity that took place during class was when Mr. Wirth explained elastic potential energy. This is when work is done in compressing or stretching a spring. Elastic potential energy is stored in the spring. As Mr. Wirth showed a very large spring compared to a tiny one, Paul Cooney noted that, "You can launch a baby off that!" There was a graph that is viewable on the notes that explains the force vs. elongation within elastic potential energy. As force increases, so does elongation. The elastic PE equation is PEs=1/2kxsquared. PEs is the elastic potential energy stored in the spring. There were four example problems that were given and reviewed. A schedule until January 16, 2008 was also given. The ticket out the door included an example from your own experience of the exchange of Kinetic Energy, Potential Energy, and Internal Energy, as well as to explain where the energy comes from and how it changes form. Homework: Blog status and worksheet number 6 on Elastic PE, which is due Monday

power=W/t

Physics Blog- 1/10

We started out on Thursday answering questions Mr. Wirth asked us. They are probably important questions to remember for the midterm, so know the answers!!
1. What is the definition of work?
We said the answer is, force acting through a distance. The equation for work is W=fd and the units are J.
2. What is the equation for kinetic energy?
KE=1/2mv squared (i cant do exponents)
3. What is the definition of energy?
Energy is the ability to do work.
4. Give an example of gravitational potential energy.
Some examples are roller coasters, alpine skiing, and power plants.

The day before the snow day or wind day or whatever that was we graphed the PE of a golf ball as it fell. As the ball fell, the PE was transformed into KE, also known as the energy of motion. The equation for the KE of the golf ball as it fell is: vf squared = vi squared + 2ad.

In this equation, vi = 0, a= g (9.81), and d= the height of the golf ball.

So.....as PE changes to KE, use the equation vf squared = 2gh.

The sum of PE and KE is constant throughout the golf ball's drop. PE+KE=constant, or as PE is lost, KE is gained.

Then, we watched a video that showed how potential energy is gained as a roller coaster goes upward. When it goes down (the fun part), kinetic energy is gained and potential energy is lost. In order to regain the potential energy, the roller coaster will have to go back up again.

Then...we learned about internal energy, which = Q. Internal energy is the total KE and PE of all atoms and molecules, including chemical and nuclear PE. Another more commonly used name for internal energy is TEMPERATURE.

The total mechanical energy = the total KE and PE of an object due to its velocity and position.

Total energy=ET (the t is supposed to be a subscript but I can't do that either). ET is the mechanical energy + internal energy. The equation for ET is: ET=KE+PE+Q.

The law of Conservation of Energy says that the total energy of a closed system is constant. A closed system is where energy is not exchanged with its surroundings. There are no external forces, and no work is done on the system.

There is also a work-energy relationship. The amount of work done=the change in PE. The work done on an object= the change in ET.

One last equation we learned on Thursday is: W=change in PE + change in KE + change in Q. The change in Q = the amount of heat added to a system. Work done against friction is lost as heat.

Andd...in case anyone forgot, the homework was Worksheet #5. Also, remember to turn in ALL LABS from the first semester, even if you don't get credit for them.