The scientific issues addressed in this lab are much the same as those found in the “Rock Drop” lab. You will need to understand the variables in the process and find appropriate ways to control them. You will need to be conscious of how measurement errors affect your predicted outcome. The context in which we will be trying to build these skills is a case of projectile motion.

Knowing how the motion of a body under constant acceleration can be described mathematically and relying on the acceleration of gravity being a constant we can glean a great deal of information about a projectile without resorting to hand timers. In the rock drop lab you may have been aware of how difficult it was to get reproducible and accurate times. Your task here will be to determine the essential features of a projectile launcher from easily accessible information. Once your launcher is characterized then you will use that information to predict the behavior of the projectile in a different situation.

An important consideration in analyzing projectile motion is the idea that the motion in the vertical direction has nothing to do with (is independent of) the motion in the horizontal direction. If you think about this in the context of a thrown object like a baseball or volleyball it seems like a silly statement. Of course what I do vertically affects how far it goes horizontally! However, the statement was made in the context of Newton's Laws. Imagine that you are pushing a box north across the floor. The box goes in exactly the direction you push it (as long as the floor is smooth!). What if the floor you are pushing across is the bed of a very large truck driving west down the road at 30 m/s? If I am pushing the box north then the northerly progress of the box is not affected by the motion of the truck. The difference is that the box also makes progress to the west as it progresses north.

A more complex situation exists if the truck is driving northwest as you push the box north. Now the truck does affect your northerly progress! This is because the two directions of motion are no longer perpendicular. In the case of projectile motion the horizontal and vertical directions are perpendicular. Because of this the motions in these two directions are independent of each other. Mathematicians call this property of independence orthogonality. It allows us to deal with projectile motion as two separate cases of 1-dimensional motion. The horizontal motion forms one case and the vertical motion is the other.

As will be demonstrated in the lab this means that no matter how fast an object is going it will hit the ground in the same amount of time as an object merely dropped from the same height. You will utilize this phenomena to determine how fast the horizontal projectile is moving when it leaves the launcher. You will also determine were it will land when launched from a different platform.

While this lab is a seriously contrived situation it has similarities that you may very well experience in your careers as engineers and scientists. The care with which you make the various measurements and how well you understand them can have great importance later on. A case in point: A fellow high school classmate of mine looked me up when I was in graduate school and we got to talking about the work he had been doing for Thiokol. As it turned out he was part of the product testing team for the solid fuel boosters used on the space shuttle. He was one of those engineers who had been called by NASA when they were trying to decide whether to launch the Challenger shuttle during cold weather. My classmate, and other engineers, felt that their data showed that cold weather launches were a very bad idea. They vetoed the launch based on their convictions about the quality of their data. Company administrators asked them if there was some way the engineers could rephrase their recommendation to NASA since this was an important flight from a variety of angles. The team was so sure about their data that they essentially refused to change their recommendation. Somewhere along the way the recommendation was watered down so that NASA felt it could make the launch with the tragic results we now know. Can you imagine how you would feel if you were unsure about the data and your administrators put this kind of pressure on you? Suppose further that someone were hurt because of your lack of confidence in your data? I personally think that the only thing that was keeping this classmate of mine from cracking in this experience was that he knew that he had tried every way he knew how to keep Thiokol from making an ambiguous recommendation to NASA. He was surely deeply troubled by the experience but I have no idea how the administrators sleep at night.

Is the story true? My former classmate surely believed it happened this way and I saw no reason to doubt him. I have never been put quite so firmly in the hot seat in my work experience but I have felt the same pressure to reinterpret my data. There is no way of know which of us will have to play this role in our lives or careers but it is a good reason to begin the process of knowing how to execute solid and believable experiments.