Studying Poppers - Computer

Poppers
Introduction
A "Popper" is a toy that consists essentially of half a handball/raquetball. Users "invert" the Popper by pressing on the top, then place it upside down on a surface. As the Popper returns to it's normal shape, it exerts a force on the surface which then exerts an equal and opposite force on the Popper. This force pushes the Popper upward and launches it into the air.

In this experiment you will investigate and characterize the force that a Popper makes on the surface as it lifts off. Using the data you obtain, you will work with additional concepts including impulse, momentum, kinetic and potential energy.

Materials
* Appropriate interfaces include LabPro, LabQuest Mini, LabQuest 1 and 2, and Go! Link

Preparing for Data Collection
  1. PlatformRemove the hook in the end of the force sensor. You'll find the thread is a standard one (6-32). Cut a square piece of wood (or plywood) that's a bit bigger than the popper and drill a hole in the center that will allow a 6-32 bolt to go through. Fasten the wood platform to the sensor, then remove the thumb screw on the other end of the force sensor, the one that can be used to hold it to a ring stand.

  2. Set the force sensor to the 50-N setting. Plug the interface into the computer, connect the force sensor to one of the analog inputs, and launch Logger Pro. Set up an experiment file with a high collection rate (≥ 200 samples/s), but a short collection time (0.1 second). Enable triggering and set it so collection starts when the force exceeds a minimum value of 5 N. Also collect 10 samples before triggering. Save this file so you can make changes as needed to fine tune it and so you can use it again next time.

  3. In practice, you'll hold the end of the force sensor firmly against the table with the wood platform on top as shown in the diagram to the right. Go to Experiment > Calibrate Sensor > Dual-Range Force Sensor. With nothing on the platform, set the value to "0" N and click on "Keep" when the voltage is stable. Put a 500-g mass on the platform, enter "4.9" N and click on "Keep" when the voltage is stable. Indicate [Done] at this point. Set the popper on top of the platform, then zero the force reading. Measure and record the mass of the Popper in the Data Table that follows.
Procedure
  1. One lab partner will hold the force probe steady against the table. A second partner, the computer operator, will start data collection. The screen should show something like "Waiting for data". A third partner, the popper operator (!), inverts the popper to store up elastic energy, places the popper on the platform, then gets ready to catch it. A fourth partner should be positioned to determine the maximum height of the Popper after it lifts off. Record that value in the Data Table.Graph

  2. When the popper unfolds, it pushes down on the platform, triggering data collection. Note that the force is not constant, but you get a nice graph showing force vs time. Another thing shown is the ringing of the sensor. The mechanism inside is similar to a bell that is tapped and it keeps vibrating for a short time.

  3. If your graph looks "chunky", you might consider increasing the collection rate. You can go as high as 1000 samples/s with modern computers with no problem. Once you have a good graph, this is the one you will work with in this lab.
Analysis
  1. Determine the area under the graph for the time while the force is positive. A sample is shown here. This is the impulse. Record it in the Data Table that follows. Approximately how long was the Popper pushing down on the platform? What was the average force during that time?

    Integral
  2. How much momentum did your Popper gain during it's liftoff? What is your calculated liftoff speed given the measured mass of the Popper?

  3. With this speed, how much kinetic energy did your Popper have when it lifted off?

  4. How much potential energy should your Popper have when it reaches the top of it's trajectory? How high should the popper have gone before it stopped rising? How does this number compare with the measurement you made during the experiment?

  5. Repeat your work and compare the second set of data with the first.

  6. Summarize the performance of your Popper in a coherent paragraph citing data and calculations from your lab.
Additional
  1. Place a measuring device such as a meter stick near where the Popper will be launched. Position a high-speed video camera so you capture an image of the popper as it reaches the top of it's trajectory. Compare this result with the one that is calculated from the impulse data.

  2. Set up a video camera so you can capture the initial launch of the Popper from the platform. You may only get 2-3 images, but from these, determine the liftoff speed. A measuring device such as a meter stick should be in the image for scale. Use the video analysis capability of Logger Pro to obtain this value. Compare the video value to the calculated value from the impulse data.

Data Table

 
 Run 1
 Run 2
 Run 3
Popper Mass
kg
      
Maximum Height
m
      
Area/Integral/Impulse
N-s
      
Liftoff Time
s
      
Average Force
N
      
Liftoff Momentum
kg m/s
      
Liftoff Speed
m/s
      
Maximum Height
m (calculated)
      



Click here for MS Word version of this lab

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Click here for a version of this lab using LabQuest

C. Bakken
November 2013