Aug'18

Experiment: Electric Cornstarch


by STEM Scouts



Written by Brooke Myers, Capitol Area STEM Scouts

 

Supplies Needed:
Balloon
Spoon or popsicle stick
Small Bowl
Cornstarch
Vegetable oil

Background:
Atoms are made up of three basic components: proton, neutron (make up the nucleus), and electron which circles around the nucleus in an erratic almost unpredictable pattern. Adding and removing protons and neutrons can cause things like radioactive decay and atomic bonds. However, removing an electron or two is an everyday occurrence in our world because they are so free-flowing. Without electrons loose structure, we wouldn’t have energy as we know it today. Students often think that electricity is different from static electricity when the basis of it is the same: electrons flowing freely.

Generally, each object is neutral. Neutral is an equal number of protons and electrons within the object. Contact with another object can transfer loosely held electrons. More electrons on the surface can cause a locally negative charge for the object that now has an imbalance of electrons. If electrons (-) leave, they create a positively charged object. The recently contacted object will contain more electrons than protons, giving it an overall negative charge.

Common Preconceptions:

  1. Charges are created with friction
    • Law of conservation of charge, charges cannot be created or destroyed.
  2. A neutral charge has no charge
    • A neutral charge is a balance between positive and negative charges giving an overall neutral charge
  3. Electricity is produced by static
    • In common terms, we use electricity as a “catch-all” term (amasci.com). Electricity is defined by the flow of electrons, which would never occur without the structure of the atom having loosely attached electrons.
  4. Positive charges can transfer
    • Positively charged protons are located in the nucleus. This doesn’t allow them to easily transfer like electrons. If we were to break apart the nucleus in any way, it would be similar to the effects of an atom bomb.

Parent Guide:

  1. A neutral object has the same amount of positive and negative charges to cancel each other out and become neutral
  2. Opposite charges attract
  3. Like charges repel
  4. Electrons are transferred from one object to another; they are neither created or destroyed
  5. A positive object has more positive charges than negative and negative charged object has more negative charges than positive charges.

Instructions:

  1. In a small bowl, mix 1/4 cup of cornstarch and 1/4 cup of vegetable oil together until the mixture is smooth
  2. Blow up and tie off a balloon. Then rub the balloon on hair or sweater until you see an attraction between the object and the balloon.
  3. Near the same spot, drip the cornstarch solution to the side of the charged area.
  4. It helps to hold the spoon horizontal to the balloon, directly across from the charged spot, about 2 inches away.
  5. Observe the attraction between the balloon and the electric cornstarch.

 

 

How It Works:

Most objects are neutral, meaning they have the equal amount of positive and negative charges. However, when an object comes in contact with another, loosely attached electrons can transfer. Like the balloon rubbing on the hair, the hair transferred negative charged to the balloon. Now the balloon has more negative charges than positive charges giving the balloon an overall negative charge. Your hair, on the other hand, has given away all of those negative charges. Now your hair has more positive charges than negative charges in that area. This gives our hair an overall positive charge. Because of the first law of electrostatics, we see an attraction between the positive hair and the negative balloon.

At an atomic level: All matter is made up atoms. Each atom is made of protons (+), electrons (-) and neutrons (0). Protons and neutrons make up the solid center or nucleus. The electrons are constantly in motion around the nucleus. Because of this, electrons can easily be transferred by contact with another object. When the balloon rubbed on your hair, it transferred all those loose electrons to the surface of the balloon. The balloon with an overall negative charge is was then attracted to the now positively charged hair. The cornstarch (neutral) caused a local attraction by the electrostatic force attracting the opposite charges in the solution (+) and repelling the like charges (-).

Summarizing Questions:

Answer the questions using evidence from the experiment.

  1. Describe the charges on a neutral object.
  2. What charges attract to each other?
  3. What charges repel each other?
  4. What happens to the electrons when two objects rub together?
  5. Describe the charges on a positive and negative object.

Cub Scout Requirements:
Bear: Super Science Req. 1& 2

TEKS Requirements:
Grade 6 (9) student understands the law of conservation of energy states that energy can neither be created or destroyed

Grade 8 (5a) describe the structure of atoms, including the masses, electrical charges, and locations of protons neutrons in the nucleus and electrons in the electron cloud.

IPC (5D) investigate the law of conservation of energy

Additional Sources & Educational Content:

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