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# Comment

Material:

## Coaster Physics App for iOS

Rating:
Used in Course: Not used in course
Submitted by: Bruce Mason (Faculty), Mar 18, 2013
Comment:

Instructors should use caution if they are using this app as a study of motion. It has several inaccuracies in both the description of the physics and in the output as it is running.

Technical Remarks:

In the introduction to the app, the following common physics misconceptions are reinforced:

The app inaccurately describes the motion of the roller coaster as "free fall" when it is constant contact with the track.

The app uses conservation of energy with no indication that this is neglecting all forms of friction and drag, a very drastic approximation for real roller coasters.

The app identifies the potential energy as a property of the car rather than the results of the gravitational interaction between the car and the earth. Potential energy is the energy of an interacting system due to the configuration of the parts.

The app defines acceleration as the change in speed, when it is the change in velocity. It incorrectly uses "positive acceleration" to mean acceleration in the direction of the velocity and "negative acceleration" to mean acceleration opposite to the velocity, a common confusion of many students.

In the description of "G-force", the app described a positive g-force greater than 1 g as being when "... you are being pushed into your seat...", when it is the increase in the normal force of the seat on the rider. Although there are different approaches to handling non-inertial reference frames, this approach will confuse students regarding forces. This is no force pushing the rider into their seat other than gravity.

While running the app, the graphs of velocity and acceleration, are not consistent in places. There are times when the velocity graph is a constant but the acceleration is not zero, and times when the velocity is increasing or decreasing linearly and the acceleration is not constant.

When the car stops, the app describes the kinetic energy as being lost to "heat energy". Current best practices in physics education reserve the term "heat" for a very different purpose, the transfer of energy from one object to another due to a difference in temperature.

Time spent reviewing site: 2 hours

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