ELECTRICAL INTERACTIONS TABLE 1: Team Roles
1. Team Member Name
3. James Barnes
5. Patience Sellers
7. Joseph Rosenthal

2.

Primary Role for this Activity
4. Manager
6. Recorder
8. Skeptic

9.
I. OBJECTIVES: The purpose of this experiment is to investigate the nature of electrical interactions using strips of Scotch tape and other common objects found in a classroom environment. By the end of this experiment, one should be able to:
● predict whether two objects will attract or repel one another or have no electrical interaction ● describe how distance affects the strength of electrical interactions.

12. II. MATERIALS & EQUIPMENT:
● Flat surface (e.g., table or book)
● Glass rod
● Pen/Marker
● Plastic rod
● Ruler
● Silk cloth
● Scotch tape
● Various objects (e.g., pen, hand, credit card, etc.)
● Wool cloth 13.
III. PRIOR KNOWLEDGE & PREDICTIONS:
Relevant things we know or assume: According to atomic theory, all atoms consist of positively charged nuclei surrounded by negatively charged electrons. The mass of a proton is nearly two thousand times that of an electron (ratio ~ 1:1836), but their charges are equal in magnitude and opposite in direction. Charge is represented by the symbol q
.
The SI unit for charge is the coulomb (C)
.
The elementary charge of a proton and an electron, denoted e, is
−19
1.602176487 X 10
C. There are two types of charges in the known universe: positive and negative. By convention, a plastic rod rubbed with wool is negatively charged. A glass rod rubbed with silk is positively charged. Like charges repel each other; unlike charges attract each other. Matter has a net charge when it contains more or less electrons than protons. However, the positive and negative charges in an electrically neutral object can be separated, or polarized, to create local regions of charge. Just because an object is polarized does not mean it has a net charge. Rubbing objects is one way of charging them. More vigorous rubbing produces larger quantities of charge. Charge can be transferred between objects when they come in contact. Conductors, such as metals, are materials through which charge moves easily. Insulators, such as plastic and
10.
11.

glass, are materials in which charge remains immobile. The potential of a substance to act as a conductor depends on how tightly its atoms hold their valence electrons. In a conductor, valence electrons are not as tightly bound and can act as charge carriers, moving freely around and between atoms. Insulators are made of elements that hold tightly to their valence electrons, preventing electron mobility.
One way to neutralize, or discharge, a charged object is to touch it. Due to its high water content, the human body is a relatively good conductor of charge. Touching an object with your hand causes the charge to be transferred to your hand. In other words, the charge is conserved. Charge, like matter, can't be created or destroyed.
Electric force is one of the fundamental forces of nature. The repulsive and attractive forces
2
exerted between charges can be calculated using Coulomb's law: F=[K(q
)(q
)]/r
, where K =
1
2
9
2 2
8.99 X 10
(N*M
)/C
. According to Coulomb's law, the force exerted between charges decreases as the distance between them increases. Countless experiments bear out this relationship.
Coulomb's law allows us to predict electric forces between charges, but it does not explain where the forces come from. The electric field model, proposed by Michael Faraday, offers a more complete picture. The field model states that the space around a charge is altered to create an electric field that can exert force on another charge that enters that field. The electric field is defined as a ratio of force to charge, E = F on q/q, which gives it units of N/C. By convention, to establish the area of a field, we imagine placing a positive charge (proton) in