- Review remaining concepts regarding complex circuits - Introduce the moon observation project and assign dates for each group to observe the moon - Operationally define and measure force, weight, mass, and density. TODAY’S OUTCOMES: ELECTRICITY SUN AND MOON FORCE, MOTION AND ENERGY

GRADING OF MORE COMPLICATED CIRCUITS 5 points: 3 points -

9. If you plug in too many things, the circuit breaker will throw. What is it that makes the circuit breaker unhappy? Why do they put circuit breakers in the house’s wiring? To much current in the circuit, which in turn generates too much power, causes a circuit breaker to “trip”. Circuit breakers are safety devices that prevent too much power from generating excessive heat that may start a fire. 10. Some students are discussing the circuit shown at right, and comparing it to the usual circuit that has just one battery. Alex says, "This is the usual arrangement of two batteries in a flashlight." Bill says, "The light bulb will be brighter than with one battery" Cheryl says, "This is about the same as carrying around a spare battery to put in when the first one goes dead." Dan says, "Nothing will happen to the battery on the left at all." Eva says, "This isn't a good idea, because it will use up the two batteries just as fast as the usual circuit with one battery." Flossie says, "This is a very bad idea. It will quickly ruin the batteries." Do you agree with any of them, or are they all wrong? The light bulb will not burn any BRIGHTER with 2 batteries in parallel as shown, but the same power will be drawn from 2 batteries instead of one, making the batteries last LONGER.

BATTERIES IN PARALLEL- SIPHON ANALOGY + + – Same pull at the base now divided among 2 sources When batteries are connected in parallel instead of series, where is the current the highest? Near the bulb (or other device(s) where voltage is “used”). Any device or element in a circuit that causes the current to slow down provides a resistance. A “short circuit” has high current, so very LOW resistance. Light bulbs, motors, buzzers, LEDs, toasters supply a resistance that can vary with voltage. The “resistors” pictured at right are made to supply a (nearly) constant resistance. What’s in the “black boxes”? “RESISTANCE” Narrowing of a tube is “resistance” to flow CURRENT IS THE HIGHEST ALONG THE PATH(S) WITH LOWEST RESISTANCE.

- How to construct a parallel circuit with any number of devices - How batteries in parallel differ from batteries in series - Lower resistance allows greater current flow WHAT YOU ARE EXPECTED TO KNOW:

Each entry must have: -date and time of the observation -circle representing the moon, with the dark part shaded -IF NOT LATE AT NIGHT, the following info on the sun: - An arrow pointing the general direction of the sun - Whether the sun is east or west of the moon - The arc measurement in degrees between the sun and moon (see bottom of page) :30pm 45°W sample (not real data)

Old Farmers Almanac Your moon today: see sunrise and set times

Assignment: EVERYONE observe the moon and record your observations either TONIGHT or TOMORROW night, as a practice attempt. Try to make your observation near sunset so you can incorporate the sun. Tonight (9/12): Moon rises 7:41 pm, sets 7:32 am Tomorrow (9/13): look on the web!

Assignment: EVERYONE observe the moon and record your observations either TONIGHT or TOMORROW night, as a practice attempt. Try to make your observation near sunset so you can incorporate the sun. -We plan on keeping records of the moon throughout the semester. -On Wednesay (9/14) there will be a sign-up sheet where everyone picks 1 of the next 43 days to do their first moon observation. -When everyone in class has observed the moon once, we will start the cycle again.

TOPICS: MOTION (MECHANICS) Force, work, energy, power Velocity and acceleration Weight and mass Gravity Friction Potential and kinetic energy

READ THE FRONT PAGE OF THE PRACTICE PROBLEM PACKET BEFORE LEAVING - UNDERSTAND WHAT IS EXPECTED OF YOU AFTER TURNING IN YOUR YELLOW SHEET TODAY: DO YOUR FIRST MOON OBSERVATION TONIGHT OR TOMORROW NIGHT, RECORD YOUR DATA

- Review remaining concepts regarding complex circuits ✓ - Introduce the moon observation project and assign dates for each group to observe the moon ✓ - Operationally define and measure force, weight, mass, and density. TODAY’S OUTCOMES: ELECTRICITY SUN AND MOON FORCE, MOTION AND ENERGY