- By
**ivie** - Follow User

- 88 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' Announcements 9/12/11' - ivie

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

Announcements 9/12/11

- Prayer
- I’ve got extra copies of the class directory
- On Wednesday I will go back and regrade all of the old clicker quizzes. As long as your clicker is registered by then, all of your quizzes will count.
- Unregistered clickers:

- 1151FBBB
- 11A3D26
- 13C413C4
- 1416FEFC
- 14710762
- 1473197E
- 160B0B16
- 16B89D33

- 190E8D9A
- 1A3B1E3F
- 1AEE0CF8
- 1B495507
- 1DAE9D2E
- 26395C43
- D68FB9E

Make sure your clicker number is not on this list!

(If it is, register it on the class website ASAP!)

Characterizing velocities

- Recall bouncing balls in jar. Focus on one type of molecule. Lots of questions, such as :
- What’s the average velocity?
- What’s the most popular velocity?
- What’s the velocity that corresponds to the average kinetic energy?
- How many molecules have velocities within a given range?

How to answer: use statistical distributions,

aka histograms

Height Histogram (made up data):

- Total students = 49
- Round heights to closest integer, plot histogram
- What is the combined area of all bars?
- If I pick a student at random, what are chances he/she will be 68 inches tall?
- What is the area of the bar at 68 inches divided by the total area?
- How many students will be exactly 68.000000 inches tall?
- If I pick a student at random, what are chances he/she will be 61.5-64.5 inches tall?
- What is average height of all students? (At least, how would you figure that out?)

“Normalized” Histogram:

- Total students = 49
- Y-axis now divided by total # of students.
- What is combined area of all bars?
- If I pick a student at random, what are chances he/she will be 61.5-64.5 inches tall? (At least, how would you figure that out?)
- How many students have heights between 61.5 and 64.5 inches?
- What is average height of all students?

Probability Distribution Function

- Imagine total # =10 billion. Tiny “bins”. Connect peaks of curve with line… becomes a function
- What is combined area of all bars?
- If I pick a person at random, what are chances he/she will be 63.6-67.2 inches tall?
- How many people have heights between 63.6 and 67.2 inches?
- What is average height of all people? (If a non-symmetric curve, this is not just the peak of the curve.)

Velocity Distribution: “Maxwell-Boltzmann”

with some constants out in front to normalize it

- At 600K, how many molecules with speeds between 400 and 600 m/s?
- What is “vmost probable”?
- What is “vaverage”?
- What is “vrms”?
- How many molecules are at exactly the “most probable” velocity?

Where does this eqn come from? Wait a few weeks.

Heat = not a fluid!

- Sir Benjamin Thompson, Count Rumford, 1753-1814
- Boiling water with a cannon

Image credit: Wikipedia

James Joule, 1818-1889

Image credit: Wikipedia

Demo/Video

- Demo: Boiling water with a vacuum
- Video: Boiling water in a paper cup

Reading Quiz

- What name do we give to the heat capacity per unit mass?
- entropy
- internal energy
- mass-pacity
- normalized heat capacity
- specific heat

Specific Heat

- Q=mcDT

Thought Question

- If you add 500 J of heat to a mass of water, and 500 J of heat to the same mass of copper, which one increases the most in temperature?
- Water
- Copper
- Same

Reading Quiz

- Thermal energy that is used to melt or freeze something is called:
- latent heat
- mass heat
- melty heat
- molar heat
- specific heat

Ice melting

100o C Water boils

Ice warming

Steam warming

Water warming

T

0o C Ice melts

Heat energy added (Q)

Phase ChangesThought Question

- If you want to melt a cube of ice that’s initially at -40C, you must first raise its temperature to 0C, and then you must melt it. Which part takes the most energy?
- Raising the temperature
- Melting
- Same

Calorimetry

- Worked problem (class designed):
____ grams of hot iron at _____ C is added to ____ g of water at _____ C in a styrofoam insulated container. What is the final temperature of the mixture? (Neglect the container.)

- ciron = 448 J/kgC
- cwater = 4186 J/kgC
- Lwater-steam = 2.26 106 J/kg

Download Presentation

Connecting to Server..