We used a dual-range force sensor to measure centripetal force. This force sensor (Order Code: DUAL-RANGE FORCE SENSOR, DFS-BTA @ $99.00) can be purchased from Vernier Software which has two ranges: ±10N or ±50N. We mounted it on a lazy susan that we purchased from a local hardware store. You may want to use a lazy susan from your own local hardware store or you may want to place your force sesnor on a turn table of an old record player. The
Dual-Range Force Sensor was connected to a LabPro (Order Code: LABPRO, $220.00). If you desire information on the LabPro or sensors, you can look on the web at http://www.vernier.com/ or cotact Vernier Software at:
Vernier Software & Technology
13979 SW Millikan Way
Beaverton, OR 97005-2886
Ph. (503) 277-2299
Fax (503) 277-2440
E-mail info@vernier.com
The LabPro has the ability to be connected to a Texas Instrument calculator or to a PC computer. We chose to connect our LabPro to a TI-83 Plus-Silver Edition Calulator. This specific calculator hlolds 1.5 megabytes of available Flash ROM and 24K of available RAM. It can hold up to 94 applications. To find out more info on TI calculators You can go to http://education.ti.com/product/tech/83pse/features/features.html.
We purchased a radio-operated electric toy car from Tower Hobby for about $175.00. However you could substitute other moving toys from your local toy store.
To do the experiement.
First connect the force sensor to channel 1 of the LabPro. Connect the TI calculator to the LabPro as well. Turn on the TI calculator. Assuming you have downloaded the DataMate software from the LabPro, hit the Apps button Scroll down to the DataMate program. Hit Enter to start the DataMate program. You will move to a screen that lists the channels. Hit one for set-up. A right triangle should be at CH 1:. Hit Enter to select the right sensor. Move to 5: Force and hit Enter or type 5. Pick te force sensor you have. This summer we used the student force sensor. We entered 4. You should now return to the previous screen and it should say that the force sensor is attached. If not check to make sure the force sensor, LabPro and TI 83 Plus are each connected.Next type in 3 to zero the device. It will ask you if you want to zero Channel 1 or all channnels. Select channel 1. It should register channel 1 and give a raw reading of some number. In our case, it was 0.227. Press Enter to zero the device. Now hit 1 (Setup) to address how to take readings. Move the right triangle to Mode by hitting the Up/Down arrow and hit Enter. Hit 2 to select the Time Graph setup screen. Now hit 2 to change the Time setting. Time between samples should be 0.5 seconds. Number of samples should be set at 200 samples. The screen will then restate what you setup and state that the experimental length will run for 100 seconds. To change the graph to read -10 to 10 Newtons press 3 to deal with advanced graph settings. Now press 2 to change the Ymin to -10, Ymax to 10 and Yscale to 1. Press 1 to accept the reading. Press 1 to accept the Time graph mode at 100 seconds. Press 1 to move to the start menu. Press 2 to start taking readings. Try this to vaerify that the probe is working. Press in and pull out slightly the force probe and observe the dots on the graph fluctuate and the digital output fluctuate. Set up the car by attaching a string from the car to the hook on the force probe. Whe you are ready to take data. Measure the radius from the center of the lazy susan where you have placed the force probe apparatus. Turn on the toy car and let it sit with the string with almost no tension. Start the counting and after about 10 seconds, get the car moving at a constant speed. Check to make sure that the lazy susan moves around at a constant rate. It appears that the lazy susan moves better when the car moves at a faster speed. You will need to develop a way to measure the rotations. This can be done several ways.
- You could use a sonic ranger or light probe to measure motion around the circle.
- You could have students use a stopwatch to determine the number of revolutions/second.
- You could have students videotape the motion of te car around the circle and then have the students analyze the data using a video analysis software packet such as Video Point.
We did the stopwatch initially to determine velocity around the circle. Then students were required to use another approach. Assuming you have access to a camcorder and video capture equipment, Video Point is an excellent option. VideoPoint is a video analysis software package that allows you to collect position and time data from digital video in the form of "video points." Data is collected by clicking on the objects of interest for each frame of a QuickTime movie. These points can be combined to form other calculations such as center of mass locations and distances between points. Furthermore, multiple reference frames can be used to analyze relative motion. You can purchase Video Point from:
PASCO Scientific
P.O. Box 619011
10101 Foothills Boulevard
Roseville CA 95747-9011
Phone: 1-800-772-8700
Fax: 1-916-786-8905
http://www.pasco.com
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