The Arbor Scientific Air-Powered Projectile was fired four times, once with each of the different thrust washers. Data for Force vs. Time was taken to detail the force exerted on the Force Plate by the base of the rocket. Details will follow. The data in this file was taken with a Vernier Force Plate, using a LabPro interface.
To gather the data, the data collection rate was set to 5000 samples per second. A triggering level of 5 newtons was set, and a pre-collection of 50 data points was set so the actual liftoff could be observed in the data. Zeroing the force reading with the rocket on top of the Force Plate was an essential step. A Logger Pro 3 file can be downloaded.
The original data was originally collected using Logger Pro 2.2 and the data plotted using Excel. A file that has been converted to Logger Pro 3 format can be downloaded.
Click here for a link to a more detailed lab that involves an entire class.
- A higher value thrust washer gives a larger maximum force to the rocket. In fact the force throughout the liftoff was larger. This was likely due to the larger pressure in the chamber needed to release the thrust washer.
- The forces are not linear, or at least the samples that were used did not display a linear behavior. If you examine the bar graph on the sheet "Maxima", you observe the four don't have a definite pattern.
- An integration of this graph gives the impulse delivered to the ground by the launching rocket. By Newton's 3rd Law of Motion, the rocket body receives an equal and opposite impulse propelling it upwards. The values one gets for the Super and Low are approximately in a 2:1 ratio. With twice the impulse, the rocket achieves twice the liftoff velocity. This gives it four times the kinetic energy at liftoff. As it converts the KE into gravitational potential energy, it rises four times higher into the air. Now basic kinematics shows that it takes twice as long to rise to four times the height (or conversely to fall four times as far). Timing the rocket yielded approximately twice the total time for the Super compared to the Low.
- All of the calculations and approximations in the previous paragraph were done neglecting air resistance which is a real force to be dealt with, especially the higher power flights.
Research done by Clarence Bakken, retired physics teacher, Sunnyvale, CA. Clarence is a consultant and trainer for Vernier Software & Technology, 12/2002.