Any input for talking to 4th graders on rocketry?

I was invited by a local elementary to do a small presentation on rocketry to 4th graders. Just wondering if anyone has any experience
talking the subject to kids this age. What should I touch on? How deep should I go into the subject? The teacher bought an Estes educator bulk pack of rockets and motors that they are going to be starting on next week. I have several videos and pictures archived on my computer that I planned on burning to disk and taking in since the school has a nice AV room with computers and overhead projectors. I am just not sure about what approach to take when speaking. Any input is appreciated.
Steve Schafer NAR #80427 L2
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The following is some of what I wrote for classroom use and then adapted for use on the original eHobbies website (when they had "Rocketry 101". It's copyrighted by me, but usable by anyone who is using it for educational purposes and not using it for business, profit, re-publication for profit.
How the Model Rocket Motor Works:
Model Rocket Motors are real miniature solid propellant rocket motors that are commercially made and tested for reliability. The consumer does no mixing of chemicals or propellant and oxidizer. Model Rocket Motors contain the following parts: a "casing" to hold everything inside, a "nozzle" to direct the flow of gasses produced, "propellant" (fuel pre-mixed with oxidizer and pressed into a solid "grain") which burns to produce huge amounts of gas, a "delay" which burns slowly after the propellant is used up to allow the rocket to coast upward and an "ejection charge" to activate the recovery system. The ejection charge blows the nose cone off of the top of the body tube in a typical model rocket and ejects a recovery system such as a parachute or long streamer. The nose cone is connected to the body tube with a shock absorbing cord (the "shock cord"). Flameproof recovery wadding is installed for each flight to protect the recovery system from scorching.
They are ignited from a safe distance using electrical igniters and a remote electrical launch controller with a removable safety key. The igniter heats up when enough electricity passes through it and this in turn ignites the propellant in the rocket motor.
"Booster" motors have no delay or ejection charge. They are designed to directly ignite another engine mounted above them for real multi-stage flights! They do this when hot gasses blow out of the top and up into the nozzle of the engine above. Obviously, the larger the nozzle of the upper engine, the more reliable it's ignition will be.
"Single Stage" motors have a short to medium delay time and are used for medium to heavy models. The heavier the model, the shorter the delay to insure that the recovery system deploys near the peak altitude ("apogee"). Too long a delay can be hazardous because you are deploying too close to the ground!
"Single or Upper Stage" motors have long delay times. They are used in upper stages of multi-stage models or in skinny lightweight models because those models will go very fast and require more coasting time to reach peak altitude.
Motor Designation Code:
The motor designation code consists of a letter, a number, a dash, and another number (and occasionally another letter that indicates special features provided by that manufacturer like small size or colored effects). Don't be confused by some motors that also have a secret manufacturing code that identifies the day they were produced (it's usually printed much smaller than the motor designation anyway).
Power Class: The letter indicates the total amount of power available in the motor class. Every time the letter increases the power class doubles. Example: a "B" motor has twice the total power of an "A" motor, and a "C" is twice as powerful as a "B" and 4 times as powerful as an "A". Model Rocket Motors are classified from "1/4A" through "G" class. Most motors are pretty close to the "full" end of their letter class, but not all. Always check the motor specifications to be sure if there is a question.
Average Thrust: The number directly after the letter indicates the average thrust in Newtons (the Metric unit of force). The higher the number the more average thrust in newtons (and the shorter the burn time of the propellant). Example: A B4 motor will thrust for twice as long as a B8 motor but it will have half the thrust. Higher average thrust motors are good for heavier models. BUT sometimes a motor has a really high initial peak thrust that drops down to a long and low thrust ("C5" motors). The motor has a low average thrust, but they can lift a heavier model. Always consult the maximum lift-off weight in the engine instructions or catalog! The maximum lift-off weight is also a function of delay time.
Delay Time: The final number after the dash is the delay time in seconds. This is the amount of time that the delay will burn between propellant burn-out and the activation of the ejection charge. Heavy or draggy models need short delays. Small, lightweight models may use longer delays.
What Makes The Model Rocket Fly Straight?:
NASA type rockets use moveable rocket engines or moveable fins to steer and stay on course. Model Rockets do not use an active guidance system. They are designed to be "stable" and keep going in the direction they are pointed. They do this because they have "fins" at the back end (like the feathers on an arrow) which guide the fast moving model through the air. All objects will tend to spin around their "center of gravity" (c.g.), or balance point. The fins create more surface area behind the c.g. than in front for the air rushing by to hit. This forces the rear of the rocket to stay in the rear. A model with fins that are too small will not be stable and will fly crazy all over the place. You can fix this by adding larger fins or by adding clay to the inside of the hollow plastic nose cone. <a link to your "Beyond the Basics" section (which hopefully has info on doing stability tests) would be nice here.> Because the rocket is not moving at the instant of ignition, we have to guide the model during the first few feet of flight as it builds up air speed. The launch pad has a "launch rod" or guide and the rocket has a "launch lug" that slides along the rod or guide.
(Do the "balloon" demo to show an unstable rocket - no fins....)
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Thanks Fred...Good stuff that I'll use in class tomorrow.
-Steve
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What is your timeframe (i.e., how long will you have with the kids)?
I've done this a few times, for grades 4-8, so if you give me a little more info I'll provide some feedback.
I figure I'm reasonable successful, as last year I had a kid in a 6th grade class who had seen me in 4th grade -- when he saw me in the classroom as he came in, I heard him shout, "COOL! The rocket guy!" <G>
David Erbas-White
Steve Schafer wrote:

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Stay away from those metal cased match-head rocket motors. lol Actually they should be cautioned on attempting to reload a rocket motor.

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