Rubbing Up Against Static Electricity

Introduction

Static electricity is the build-up of electrical charge in an object. Sometimes static electricity can suddenly discharge, like when a bolt of lightning flashes through the sky. Other times, static electricity can cause objects to cling to each other, like socks fresh out of the dryer. The static cling is an attraction between two objects with different charges, positive (+) and negative (–).

You can create static electricity by rubbing one object against another object. This is because the rubbing releases negative charges, called electrons, that build up to produce a static charge. For example, when you shuffle your feet across a carpet, you are making many small contacts between the surface of your feet and the carpet, allowing electrons to transfer to you, building up a static charge on your skin. You can suddenly discharge this static charge as a shock when you touch a friend or some objects. Similarly, when you rub a balloon on your head it causes opposite static charges to build up in your hair and in the balloon. You can see these two opposite static charges attracting each other when you pull the balloon slowly away from your head making your hair stand up, as shown in Figure 1, below. 

Figure 1. Static electricity makes your hair stand up! (NASA, 2004)

In this experiment you will test if the number of rubs can change how long the static charge will last by rubbing a balloon with wool and timing how long it will cling to a wall. Wool is a material that readily donates its electrons, so when you rub the balloon with it it will donate its electrons to the surface of the balloon, giving part of the balloon a negative charge. The wall should normally have a neutral charge, but the charges within it can rearrange so that a positively charged area is interacting with the negatively charged balloon, causing the balloon to stick to it. By doing this experiment you can investigate how effective rubbing wool against a balloon is at creating static electricity and a static charge.

Terms and Concepts

• Static electricity
• Charges
• Electrons
• Static charge
• Attraction

Questions

• How does friction produce static electricity?
• How is static electricity related to charge?
• How can you measure static electricity?

Bibliography

• Science Made Simple. (n.d.). Static Electricity: What Causes Static Shocks? Retrieved March 18, 2006 fromhttp://www.sciencemadesimple.com/static.html
• Museum of Science, Boston. (n.d.). Static Electricity: Electricity Medley. Retrieved June 19, 2014, from http://www.mos.org/sites/dev-elvis.mos.org/files/docs/education/mos_observing-electricity-magnets_electricity-medley.pdf
• The Library of Congress. (2011, June 1). How does static electricity work? Everyday Mysteries. Retrieved June 19, 2014, fromhttp://www.loc.gov/rr/scitech/mysteries/static.html
• Brynie, F.H., 2005. Parents Crash Course: Elementary School Science Fair Projects, Hoboken, NJ: Wiley Publishing Inc. pp 124-130.

Materials and Equipment

• Balloons (at least 3). Smaller balloons, like water balloons, may work better in humid environments, but you will still blow the balloons up with air.
• Woolly sweater, scarf, or blanket
• Stopwatch
• Lab notebook

Experimental Procedure

1. For this experiment, you will need a data table for your results. You will need one data table for each trial, so make at least three data tables for doing at least three separate trials. You can use a data table like Table 1.

Number of Rubs	Stays on Wall? (Y/N)	Time on Wall (seconds)
1
2
3
...

Table 1. You can use a data table like this one to write down your results.

2. Blow up the balloon and tie off the end.
3. Rub the balloon on the scarf once, in one direction.
4. Hold the balloon up on the wall, start the stop watch and release. Does it stay on the wall? If not, stop your stop watch and write "0 seconds" in your data table.
5. Touch the balloon to a metal object. This should discharge any extra electrons into the metal.
6. Repeat steps 3 to 5, increasing the number of rubs each time until the balloon sticks to the wall. When you increase the number of rubs do not rub the balloon back and forth, but instead always rub the balloon in the same direction each time.
7. When the balloon does stick to the wall, keep the stop watch going until the balloon falls off of the wall. When it does, stop the stop watch and write the time in the data table next to the matching number of rubs.
8. Repeat step 7, increasing the number of rubs each time and recording the amount of time the balloon sticks to the wall with the stop watch. Write the results in the data table each time. You can continue increasing the number of rubs until you have several data points for the balloon sticking to the wall.
9. Make a graph of your results. You can make your graph by hand or you could use a program like Create a Graph to make it on a computer and print it out. A line graph is the best type of graph for this experiment. Make a scale on the left side of the graph (Y-axis) for the time in seconds, and a scale on the bottom of the graph (X-axis) for the number of robots. For each point of data, make a dot where the number of rubs and the time in seconds intersect.
10. Analyze your results. Does your data make a line? Does the line go up or down? Does the line level off at some point, or keep going? Does the time the balloon stays on the wall increase or decrease with the number of rubs?
11. Repeat steps 2–10 at least two more times so you have done a total of at least three trials total. Does the data for each trial match with the previous trials?