BACK STORY
IDENTIFYING A NEED
This project started with two goals. One sought to produce a versatile tool that could be used in various real-world situations such as moving up and down on elevators or attached to an object following a circular path on a turntable or oscillating at the end of a pendulum. Ultimately, this tool would help students of physics reconcile common misconceptions in a way that wasn't overly contrived. This leads to the second goal; to engage students as the makers, testers, and continual developers of such a tool and the senarios in which they use it.
Central to these goals is the low cost accelerometer, a tiny electromechanical sensor that is prolific in nearly all mobile devices. To determine how accelerometers can be used in the classroom we first need to understand what is needed and what must be avoided.
Consider the following example.
A MISCONCEPTION THAT’S QUITE COMMON
Watching astronauts “floating around” on a space station, most people are quick to exclaim that the astronauts are “weightless”. However, astronauts still have weight even while in orbit in space. It's the force that normally holds them up on Earth that is absent and therefore it's more appropriate to say the astronauts are in "free-fall".
HOW ACCELEROMETERS ACTUALLY WORK
If astronauts could look at an acceleration-meter, it should indicate that their weight is pulling them into a circular orbit detectable with a centripetal acceleration. Unfortunately, accelerometers don’t calculate acceleration based on the position of the astronaut and time, but by sensing the response of a tiny inertial mass to external stimulus.
WRONG TOOLS REINFORCE MISCONCEPTIONS
If an astronaut used a common low cost accelerometer found in nearly any mobile device while floating around on the space station, it would actually show zero acceleration. Applying Newton’s Laws, anyone would be justified in saying the total force acting on the astronaut is zero and wrongly concluding that there is no weight.
A TOOL THAT SUPPORTS WHAT'S OBSERVED
This project takes advantage of what the accelerometer actually measures with illustrated representations of contact forces in what we call a normalometer /ˈnɔrm(ə)lɑmətər/. Now, an astronaut using a normalometer would see that there is no normal while they are in free-fall, which would be correct.
