The Terminal Velocity Lab is a software simulation where students will graph the velocity versus time for four balls of different materials and densities and find their terminal velocities (if possible).
The simulated equipment is a long glass or plastic tube through which the balls are dropped. The balls are aluminum, cork, styrofoam, and aping pong ball. The time to fall is measured by a set of photogate timers. The top photogate is set, to keep the initial velocity equal to zero. A number of data points are taken, moving the bottom photogate each time.
The simulation has been made as close to reality as possible. Students need to center the ball in both the x and y directions, keep the ball close to the top of the tube before dropping, and not break the top photogate before dropping. This also assures that students get good data.
After calculating the velocities of the balls, students make a graph of velocity versus time. The terminal velocity can be read off of the graph where the curves become horizontal. The lab handout includes a series of questions that lead students to see that the area under the graph is equal to the displacement of the balls moving down the tube.
The software simulation includes directions to students on how to run both the simulation and lab procedures.
A sample lab answer key is provided.
All of the files are provided in a Zip file. Extract the files and double click on the html file to start the software.
A list is given below:
Software: TermVelLab.html and TermVelLab.swf
Requirements: PC or MAC computer, Flash player
This file: InstructorsNotes.doc
Lab Handout: TermVelocityLab.doc and PDF
Lab Key: TermVelocityLab_Key.doc and PDF
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This lab was developed due to some difficulties running the real life lab in the classroom. We first purchased plastic tubes, but they discolored and we had to cut holes in the side so the photogates would work. We later moved to long glass tubes which were prone to breakage especially by the balls bouncing off of the table back up into the bottom of the tubes. The setup was quite difficult to construct with clamps for the tube, the timer, and the photogates.
Add to that the fact that students often got very poor data. They found it difficult not to break the top photogate early. The lighter balls were subject to air currents and the lightest balls were actually seen to rise in the tube. The balls also had a tendency to bounce back and forth against the sides of the tube as they fell.
The final straw was the lack of science classrooms which led to multiple classrooms and preparations. This led to the simulation software.
Note that the data and curves will not be perfect. The ball can be dropped in a small but important window of distance above the tube, leading to noticeable data error.
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