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The Caliper
Baking Soda/Vinegar Reaction Revisited
The reaction between baking soda and vinegar can be followed in a number of ways: change in temperature, change in pH, or change in pressure (if you conduct the reaction in a sealed vessel). This activity describes a new method—using an Ohaus Scout Pro™ balance to measure the mass change as the reaction proceeds.
OBJECTIVES MATERIALS
SUMMARY OF THE PROCEDURE
DATA ANALYSIS 
Analysis of baking soda and vinegar reaction
Blue and Pink: The Effect of Temperature on the Cobalt Chloride Equilibrium System
About once a month, we receive a good suggestion of a chemistry experiment from “retired” teacher, Walt Rohr (Easton, PA). Here is one of his ideas for using a Temperature Probe and Conductivity Probe to monitor a well-known equilibrium reaction:
Co(H2O)62+(aq) + 4Cl–(aq) ↔ CoCl42–(aq) + 6H2O (l) sH = + 50 kJ This reaction makes a great demonstration during your equilibrium studies in the spring. Since it is endothermic in the forward direction, a temperature increase results in the formation of additional products and the appearance of blue color (due to the CoCl42- ion). Of course, cooling off the reaction favors the reverse exothermic reaction, returning the color to pink (due to the Co(H2O)62+ ion). Walt noticed that there are unequal numbers of ions in the reactants and products of this reaction: 5 ions in the reactants, 1 ion in the products. As a result, he thought there might be a noticeable conductivity change as the reaction created more products or more reactants. This equilibrium system is prepared by dissolving 1 g of solid CoCl2 • 6H2O in 170 mL of denatured (95%) ethanol (in a 250 mL Erlenmeyer flask). The solution is initially blue. Slowly add distilled water to it until it just turns pink (indicative of Co(H2O)62+). You will also need two 1 liter water baths, one with 500 mL of hot water at about 70°C, and the other with a mixture of crushed ice (or ice cubes) in 500 mL of water. The handles of the Conductivity Probe and Temperature Probe can be bound together with several wraps of a rubber band. The Conductivity Probe is set to the 0–2000 µS/cm range setting. The probe combination can be placed into the Erlenmeyer flask and solution. Start up your data-collection program so the two probes auto-ID, and use a data-collection rate of 6 readings/minute for 10–15 minutes. 
Temperature and conductivity changes in cobalt chloride reaction
Collect temperature and conductivity data for about 1 minute at room temperature and then place the flask and probes into the hot-water bath. Once in the bath, the contents can be swirled (or, for less disturbance, add a magnetic stirring bar to the flask, and place the flask and liter beaker on a magnetic stirring plate). After 3 minutes, the color will change from pink to the deep blue of CoCl42-. Notice in the data shown here, as the temperature increased, the conductivity simultaneously decreased, due to fewer ions in the products. Next, transfer the flask and probes to the ice-water bath, and see what happens to the equilibrium. As seen in our data, conductivity increases as the temperature drops, due to the formation of additional ions in the reactants (containing the predominantly pink Co(H2O)62+). Your students may wonder if the temperature change alone could be the cause of the changes in conductivity. We were curious too (even though our Conductivity Probe has built-in temperature compensation). We performed a control run using sodium chloride solution in similar water baths and found only a small change in conductivity due to temperature. Extension: You may want to try taking a digital movie of this demonstration, and use the video-synchronization feature of Logger Pro 3.3 to create an experiment file with the movie and data synchronized. “Go Forth and Measure” at MIT
One of the core courses in the Mechanical Engineering Department at MIT is the junior-level course, 2.671, Instrumentation and Measurement. This 50-year old course has been significantly redesigned in the last several years by Professor Ian W. Hunter, Director of the BioInstrumentation Laboratory at MIT. The underlying principle for the course redesign was that undergraduate education should be an interactive experience. The LabPro system and sensors from Vernier are perfectly suited for giving students the opportunity to make measurements, both during lecture and on their own. At the first lecture each term, students are given an assignment called “Go Forth and Measure.” Unlike the scripted experiments prepared for them in the laboratory component of 2.671, the measurements they make for this assignment are only limited by their imagination and the capabilities of the sensor or sensors. Each student in the class of about 50 is given a LabPro unit and one or more sensors. 
The most popular sensor is the 3-Axis Accelerometer, which students have used to study hand motion while playing the piano, the motion of balls while juggling, the acceleration experienced by a gymnast, and a freestyle skier during flips and twists. One student used the Microphone to look for differences in the sound emitted by her cat in different moods! Another topic that has inspired the students is the measurement of CO2 concentration. A student who measured the difference in CO2 levels for sleeping vs. awake mice commented that the most tedious part of the experiment was waiting for the mice to fall asleep. Another student’s report titled, “When a Scientist Becomes the Cricket,” described measurements of the CO2 concentration in his poorly ventilated room during the night. Luckily for him, he terminated the experiment and opened his door before morning! Finally, an enterprising student decided to examine her sleeping patterns during lectures (not 2.671 lectures, of course!) by measuring CO2 levels at different locations in the lecture hall. She found that CO2 levels were initially higher and increased more rapidly at the back of the large lecture hall, which could explain her tendency to fall asleep while sitting at the back. We are delighted to be able to provide the students with inexpensive, easy-to-use products that allow them to “Go Forth and Measure!” A Moving Glacial Study
Here’s a story about a really cool—literally—use of Vernier equipment. Robert Schlichting of Cleveland HS in Portland, OR, has been taking some fascinating data on the process of glacial ablation; that is, how quickly the surface of a glacier recedes due to solar radiation. 
As a part of a larger study on the energy budget of a rock debris-covered glacier, Schlichting wanted to measure the change in height of the top of the glacier as a function of time. A Motion Detector, usually used to follow the motion of a rapidly moving cart or ball, was used to measure the distance from a fixed point to the debris on the surface of the glacier. Of course, the surface of the glacier doesn’t move very fast, and therein is the challenge for this data-collection effort. In order to collect data remotely for a long period of time (two weeks or more), Schlichting needed to provide for additional power to the Vernier LabPro. He built a solar charger for a 6 V gel cell battery system and used this to supply power to the LabPro. The charger, LabPro, and Motion Detector were all mounted in a plastic bucket for protection from the elements. The downward facing bucket and detector were then mounted on a deeply set post. The location chosen was the Eliot Glacier on one of our local volcanoes, Mt. Hood. The data-collection parameters were set to one point every 15 minutes, over a period of 14440 minutes (10 days!). Note several interesting things about the results shown below:1) The glacier lost about 10 cm each sunny day. 2) In September, some early season snow added depth to the glacier. 
Level of snow field as a function of time
Make Physics Fun with Bridge-Building Contests
When I taught high school physics, I had the students build model balsa-wood bridges. The goal was to make the strongest bridge spanning a specified distance with a certain mass limit (and some other restrictions). The contest was always a big hit with the kids, and it really helped bring attention to the physics program. The actual testing of the bridges was difficult, and it lead me to do my first experimentation with force sensors, using strain gages. With the introduction of our Force Plate a few years ago, bridge-building contests became a lot easier. Jeff Hellman, Elmira HS, Elmira, OR, recently had such a contest. He reported on it at the recent meeting of the Oregon section of AAPT. As the diagram below shows, Jeff made a U-shaped structure out of wood to support the bridge. This structure sits on the Force Plate. As force is applied to the bridge, the Force Plate records the force. Jeff used a scissor jack to apply the force to the bridge, and he built a wooden outside frame to support the scissor jack. This is shown in the photo below. As force is applied to the bridge, the Force Plate records the force. Note that you can easily set up a column for “maximum force” in Logger Pro, so that even when the bridge breaks, the largest reading is noted. This makes for a great spectator sport. For more details about this contest, see Jeff’s web site at www.sciteacher.com/bridges. One more personal note: the person who introduced me to the idea of bridge-building contests for physics classes (in 1975) was Jeff’s father, Walter Hellman (physics teacher at Hillsboro HS, Hillsboro, OR). 
Physics students from Elmira HS show their creations
NASA Student Launch Initiative
The NASA-sponsored Student Launch Initiative (SLI) asks high school and college students to design, build, test, and ultimately launch reusable rockets carrying scientific payloads. At the high school level, several schools compete to construct a vehicle that is designed to reach an altitude of one mile above ground level. The Vernier LabPro and a variety of Vernier sensors are being employed by a few of this year’s participants. For more details check http://education.msfc.nasa.gov/docs/127.htm LabPro as a Digital Multimeter
An article in the October 2004 issue of The Physics Teacher journal explains how to build an auto-ID resistance probe for use with LabPro. Robert C. Word and Erik Bodegom, from the Department of Physics at Portland State University, and Ian Honohan (Vernier Software & Technology) found that the home-made resistance probe can accurately measure electrical resistance in the range of 100 to 1 M. Along with Logger Pro software, a Voltage Probe, and Current Probe, the LabPro can perform the job of a digital multimeter. On the Halfpipe
The Discovery Channel holds a competition for middle school students who won their regional science fairs. The students went through several challenges, among them the skateboard physics task. The question asked of the students was this: where, during the ride, is the halfpipe pushing on the rider the most, and where is the force the least? To make these measurements, the riders carried a Vernier 3-Axis Accelerometer connected to a Vernier LabPro. A standard video camera with a video capture board provided images to synchronize with the acceleration data in Logger Pro. We created a calculated column that is the square root of the sum of the squares of the individual acceleration values, yielding the net or scalar acceleration values. Scalar acceleration with an accelerometer corresponds to the perceived g-factor. 
Because the accelerometer responds to both kinematic acceleration and the Earth’s gravitational field, the scalar “acceleration” is 9.8 m/s2 when the device is at rest. The measurement is really the Normal Force per Unit Mass, which we’ll call the g-factor for short. Kinesthetically, the g-factor corresponds to the compression one feels in the legs during snowboarding. You feel a g-factor of 9.8 m/s2 (or 1 g) when standing still. This g-factor measurement is exactly what we needed to confirm the student predictions as to where in the halfpipe the forces were large, and where they were small. To make your own prediction, you’ll need the skater talk: the halfpipe includes the vert, or vertical wall; the coping, or the railing at the top of the vert; the transition, which is the curved part of the pipe; and the floor, which is the flat part at the bottom. What is your prediction? Go to www.vernier.com/innovate/innovativeuse33.html for a video of the Logger Pro screen, showing both the video of a BMX biker, and the synchronized accelerometer data. Was your prediction correct? Our thanks to the Discovery Channel for inviting us on this data-collection expedition! Ideas from The Physics Teacher
The Physics Teacher journal often has many great ideas for teachers. Quite a few of them relate to using our products. Here are some recent examples: “How About a Magnet and a Paper Clip?—Experiencing the Interaction Forces Kinesthetically” by Hans Pfister, Dickinson College, Carlisle, PA, in the February 2005 issue takes the Newton’s third law demonstration to a new level. “Inductively Modeling Parallel, Normal, and Frictional Forces” by Edward P. Wyrembeck (a former Vernier Technology Award winner), Howards Grove HS, WI, in the February 2005 issue, has his students model forces on an inclined dynamics track. “Deconstructing Black Box Aspects of a Computerized Physics Lab” by William P. O’Brien Jr., Southwestern University, Georgetown, TX, in the March 2005 issue, offers suggestions on how to introduce the use of computerized data-collection equipment in your classes. “Fan Unit Physics” by Robert A. Morse, St. Albans School, Washington DC, in the March 2005 issue, explains how to do several good demonstrations or labs using dynamics carts with fans on them. “The Effect Surface Temperature Has on Kinetic Friction” by Peter Kauffman and Mark Vondracek, Evanston Township HS, IL, in the March 2005 issue, does a unique study of friction on a heated griddle. For more innovative uses, see www.vernier.com/innovate
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The halfpipe used by skateboarders and BMX bike riders allows for some spectacular tricks. Given that the riders can rise nearly two meters above the top of the pipe, which is itself about three meters high, the forces and accelerations must be fairly large.