Say you Put Some Coffee Beans by a Van de Graff

Per.3A, 1/17/07

• 2.1 Background Information

• 2.2 Review of Literature

• 2.3 Question

• 2.4 Hypothesis

• 2.5 Materials

• 3.1 Procedures

• 3.2 Problems/Solutions

• 4.1 Results

• 5.1 Discussion

• 6.1 Bibliography

• 7.1 Additional Information

• Back to Research

2.1) Background Information:

            Our experiment is based on the properties of a Van De Graff, which creates a strong amount of static electricity using a motor to drive a pulley. The pulley obtains a negative charge from the belt on the inside by a process called triboelectrification. Devices used in a classroom setting are capable of producing up to 80,000 Volts. The spherical nature of the Van De Graff creates a charge that is equally distributed throughout the surface. It continues charging up and eventually becomes ionized, which is sometimes called electric wind due to the physical movement of the air. When this air is disturbed, it creates potential to release the magnetic charge into static electricity. Using this magnetic force, Van De Graffs are able to attract opposite or neutrally charged particles, such as Styrofoam, plastic, and hair.       

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2.2) Review of Literature:

            Whenever electrons come to a point, they create ionic wind. This wind can be reduced by the Van De Graff’s spherical design, allowing the electrons to be evenly dispersed (Rueckner 2004). Robert Jemison Van de Graaf was one of the first people to dive into the field of electrostatics. His mechanism allowed a motor to drive a belt, which carried electrons up the belt (Giancoli 1998). Electrostatics is the study of charges mainly at rest, and the effect it creates on non-conductors (Elfick 2006). By removing the electrons in positively or neutrally charged particles, this movement can occur (Brock 2004). To keep the movement consistent, the use of neutrally charged particles provides the best results. Some of these items include: silk, glass or plastic rods, fur, pith balls, resistors, charging plates, packing peanuts in a Ziplock bag, and a ping pong ball on a string (Aeschliman 2002). The use of coffee beans provided not only for easily manipulated particle size, but sub-par movement when the Van De Graff was on full blast.

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2.3) Question: Will surface area affect the time in which particles become attracted to a Van de Graff generator?

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2.4) Hypothesis: If the coffee beans are ground longer, the Van de Graff generator will more quickly attract them because the increased surface area will allow each particle to become charged faster.

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2.5) Materials:

Van De Graff Generator

200 Coffee Beans

Coffee Bean Grinder

Stopwatch

3x8x6 cardboard box

36x18x18 plastic laundry basket

spatula

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3.1) Procedure:

            Split the 200 coffee beans into five groups of 40. The five groups represent the differing levels of grinding the beans will undergo: 0 seconds, 10 seconds, 20 seconds, 30 seconds, and 60 seconds. These five groups now must be split into four subgroups of 10.  There will be 4 trials for each level of grinding, and different beans must be used for each trial to ensure that the beans aren’t prematurely charged. This would affect the time it would normally take for them to react to the charge of the Van de Graff.

Now that the whole beans are split into their respective groups, use the coffee grinder and stop watch to grind the groups of 10 according to their predetermined levels. Set the timer to count down, and release the grinding when the time is up. Some grinding will continue immediately after as the machine winds down, but this residual grinding is consistent and thus not a significant factor. Label these groups according to their time ground, so they can be quickly identified during the experiment.

            Stack the cardboard box atop the laundry basket and position flush against the Van de Graff. Though the bases touch, there will be space between the cardboard box and the sphere of the Van de Graff. This is fine; when the beans are on the box there will need to be 5 inches of space anyway. Place the first group of beans ground for 0 seconds on the cardboard box. As noted above, measure accurately that they are 5 inches away from the actual machine. Use the spatula to position them in a straight, roughly level line. This attempts to create equal opportunity for the beans to be charged. Turn on the Van de Graff simultaneously with the stopwatch. Immediately stop the time when the first particle is attracted and drawn to the sphere of the Van de Graff. Solitary movement limited to the platform itself should be ignored. If there is no movement after 3 minutes, turn off the machine. After the trial, the beans should be discarded or removed, as they will not be used again. The spatula efficiently cleans the platform of the previous bean particles. Repeat this process for each group, progressing from 0 seconds to 10 seconds, 20 seconds, etc… At the conclusion of the experiment, there should be data for 4 trials from each of the 5 grinding levels.

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3.2) Problems/Solutions:

We had originally used plastic cutting boards to transfer the coffee grindings from the grinder to the platform next to the Van De Graff, and just kept the grindings on the cutting boards. But we quickly found from our preliminary testing that the plastic cutting boards took charge from the grindings, which skewed our data. In order to generate correct data we removed the plastic cutting boards from the equation. Immediately our data improved.

At one point the Van De Graff stopped charging and attracting particles, so we tried multiple things to remedy its deficiency. First we thought that there might be other things on the Van De Graff that hindered the charge before it could reach the coffee bean grindings, so we cleaned off the sphere of the generator with foaming window cleaner. Although it didn’t totally solve the problem, we think that cleaning the Van De Graff helped. Next we thought the power outlet that the generator was plugged into was too hot or had changed its power output, so we switched the outlet that the Van De Graff was plugged into. Again, the switching of outlets didn’t solve the big problem, yet minor improvements soon followed. After that we decided to move the Van De Graff generator from a table to the floor of the kitchen, because we thought that the table might have acquired charged after so many tests and it consequently was struggling to ground the current. After moving the Van De Graff onto the floor it thankfully began to work again and give relatively good data, so we conjectured that it was a partial combination of everything we did that caused the Van De Graff to work again. 

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4.1) Results:           

            Some of the uncertainties included the varying size of beans due to nature, varying size of particles resulting from inconsistent grinding, human timing error, human grinding-release error, inconsistent Van De Graff charge, air resistance, humidity, and grounding of charge in between trials.

            Below the first round of data is documented. This series of trials was riddled by problems with the Van de Graff itself and its surrounding environment. The little data it did forfeit was inconsistent, inconclusive and skewed.

            The graph directly below that one records the data, which was observed after certain problems were addressed and relatively contained. It appears to demonstrate the tendencies projected by the various theories concerning the Van de Graff.

First “Bad” Data Set .:. Data File (text - tab delimited)

Second “Good” Data Set .:. Data File (text - tab delimited)

Second “Good” Data Graph

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5.1) Discussion:

The data that we collected, though skewed in some spots, supported the original hypothesis that a greater surface area due to longer grinding periods would increase the rate of particle charging and decrease attraction time. The data, illustrated below, shows that the attraction time largely decreases as the grinding time increases proving our hypothesis. At the 20 second grind-time, the average time is greater than the average 10 second-grind time, but only by a small amount so it does not seriously compromise the rest of the data. Further research could investigate the time it takes to attract the entirety of the coffee grindings to the Van De Graff. Also, other materials such as beans or Styrofoam would provide interesting theses inquiring whether attraction would be faster or longer. Further research could also try to eliminate some of the errors and mistakes inherent in this type of experiment, and therefore yield more accurate results.      

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6.1) Bibliography:

Aeschliman, Ralph. Electrostatics.

<http://www.physics.wsu.edu/demos/EandM/electrostatics.HTM> 2002.

Brock, Jeff. Static Electricity.

<http://www.bu.edu/lernet/GK12/jeff/Unit/Lesson4.htm> 2004.

Elfick, J. Electrostatics, static electricity, attraction and repulsion.

<http://www.uq.edu.au/_School_Science_Lessons/UNPh31.html#31.0.0> 2006.

Giancoli, Douglas C. Physics: Principles with Applications. Prentice Hall. Upper Saddle River, New Jersey. 1998.

Rueckner, Wolfgang. Electricity and Magnetism.

<http://www.fas.harvard.edu/~scidemos/xml2html.cgi?section=em> 2004.

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7.1) Additional Information:

1) http://www.indiadaily.com/editorial/4572.asp - An article that describes patterns of electromagnetic attraction and repulsion in full detail.

2) http://www.patentstorm.us/patents/5687823-claims.html - An explanation of an electromagnetic clutch.

3) http://amasci.com/emotor/vdg.html - Information on the use and handle of a Van De Graaff generator.

4) http://www.howstuffworks.com/vdg.htm - An informative website on Van De Graaff generators and the general principles behind their functioning.

5) http://www.mos.org/sln/toe/history.html - The history behind the mass production of what we know to be the Van De Graaff generator..

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