**Day 3**

**Calculate the G-force experienced by a model rocket (by analyzing a video clip)**. You can click here or here or here to download a video file suitable for video analysis. If you need the acceleration tutorial (handed out in class), click here. This day is set aside for the analysis of a video recording of a launch. To begin the analysis, you need to make an Excel spreadsheet of time vs. distance based on data extracted from the video. Roughly, here are the key principles/challenges to keep in mind.

- How are you going to measure the rocket's position as a function of time from the video (that is, both distance AND time). Hint: Quicktime can report the time of each frame but if the movie is shot in slow motion (which this is), then you will need to divide the time by the appropriate factor (ask Dr Don since it was his camera that was used).
- Do you remember any formulas involving force? How about F=ma? This formula says if you know the mass of an object and it's acceleration, you can calculate the force. Mass is easy, right? (actually, you will have to make some assumptions so be sure to think it through). But how do we get a handle on acceleration?
- Acceleration is the rate of change of velocity. So if we knew how the velocity of the car was changing, we could calculate accelerations. Can you measure the velocity of your rocket from the video data as a function of time? How?
- Any good experiment includes a prediction for what you expect to happen (it's called a "hypothesis"). Can you sketch a graph of velocity as a function of time that you expect to observe? How about acceleration vs. time?
- To summarize, you will start with a graph of distance vs. time using data taken directly from the video. From this, you will derive a second graph of velocity vs. time. From the velocity graph, you can derive an acceleration graph. Once you have acceleration as a function of time, multiplying by the mass gives you a force. How does this force compare to the force of gravity?

HINT: An easy way to access the time for each video frame is with Quicktime Player. Turn on "Show Movie Inspector" (under the Windows menu) and the time for each frame will show up as you slew through the clip. You are on your own to find a way to measure the distance traveled by the rocket (to be most accurate, you need to account for any motion of the camera and parallax).