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Dryer Sheets

Dryer Sheets

The old saying "opposites attract" is true not only in romance, but also in chemistry and physics: positively charged particles are attracted to negatively charged particles. In this Science Update, you'll find out how this relates to your laundry.


Transcript

Making clothes less clingy. I'm Bob Hirshon and this is Science Update.

Perhaps an annoying experience with static cling prompted Kevin Ambrose of Washington, D.C., to e-mail us this Why Is It question. He wants to know how dryer sheets help keep clothes from sticking together in the laundry.

Well, Kevin, we asked Benham Pourdeyhimi, a textile engineer at North Carolina State University in Raleigh. He says static builds up when fabrics rub together and exchange electrons. Some surfaces get positively charged, and others get negatively charged, so they attract one another.

Pourdeyhimi:

The static electricity that's generated can be as much as 12,000 volts. And this static charge causes your clothes to cling together.

Pourdeyhimi says dryer sheets contain positively-charged ingredients that are released by the heat and tumbling motion of the dryer. These ingredients bond loosely to any negatively-charged fabric surfaces—neutralizing the charge and acting as a lubricant.

Pourdeyhimi:

Basically the fabrics now have similar characteristics on both sides, and you no longer have this exchange of electrons, and the material will not have static cling problems.

If a science question's got you charged up, call us at 1-800-why-isit. Or e-mail us from our website, www.scienceupdate.com. For the American Association for the Advancement of Science, I'm Bob Hirshon.


Making Sense of the Research

Static electricity doesn't just happen in the dryer. You can see it in many other situations, like when you walk across a dry carpet and then touch a metal doorknob, or when you rub two balloons together. In every case, though, some kind of friction is involved.

Although static electricity depends on friction, it isn't caused by friction itself. Rather, it's caused by adhesive forces between the molecules on the surface of the materials. To use laundry as an example: Your socks, like anything else on earth, are made up of atoms. Each of these atoms can be pictured as shells of electrons orbiting a nucleus.

As you might remember from chemistry class, there's a maximum number of electrons that can fit in each shell (usually eight). Atoms are more stable when their outer shell is full. Atoms crave this stability so much that if two atoms brush against each other, they'll try and share or exchange electrons in order to balance themselves out. That makes the atoms, and your socks, stick together—in other words, it creates static cling. When you pull your socks apart after a spin in the dryer, the crackling static electricity comes from the sticky surface electrons being yanked away from each other.

Dryer sheets pre-empt static electricity by releasing positively charged particles that satisfy the cravings of negatively charged surface atoms on your laundry. So now the negative surfaces are more positive, and therefore they're not so attracted to the other positive. The results? Less electron exchange, less adhesion, and less static cling.

Now try and answer these questions:

  1. What are adhesive forces?
  2. Explain how friction and adhesive forces relate to static cling.
  3. How do dryer sheets prevent static cling?
  4. Suppose dryer sheets produced negatively charged particles instead of positively charged ones. Would the result be the same? Why or why not?

For Educators

Static Electricity is a four-part lesson by Science NetLinks for grades 6-8.

For older students, The Physics Classroom offers this detailed primer on static electricity.


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