Coulomb's Law

In the following activity, we each took a 10cm strip of scotch tape and stuck the sticky side down onto the lab table. We then peeled the strips off of the table and observed how the strips reacted when placed close together. When the strips are far apart, the attraction is small. When the strip are close, they attract each other stick together. 

Next we took another two 10cm strips of tape and stuck the first one, labeled B, onto the lab table and the other strip, labeled T, on top of the first strip. Then we pulled the strips apart and observed the reaction between the two strips. Strip T was more attractive than strip B. The strips now repelled one another. 

Electrostatic forces are the forces between particles that are not moving or are moving very slowly. Below are pictures of the video application depicting the movement of a charged particle in relation to another.

This is the initial starting point of the two balls.

As the ball on the stick is moved towards the other, the other moves away slowly. There is clearly an electrostatic force between the two balls.

Below is a free body diagram of the above pictures.

By using the summation of the forces in the x and the y direction, we were able to solve for the force acting on the ball connected to a string hanging.

The drawing of a graph below shows the relationship between force and separation distance between two charged particles. 

Below are some conclusions gathered by the above activity. We used Coulomb's Law to solve for the magnitude of charge.

It is impossible to determine the charge of each particle because they both repel each other. Some sources of uncertainty could be that we did not find the center of mass of the balls.

Below is an actual graph depicting the change is force relative to the separation distance between two charged particles. The force quickly decreases as the separation distance increases.

Activity: Using Coulomb's Law for Calculations

Consider two charged objects lying along the x-axis. A 2.0 x 10^-9 C point charge is located at x=3.0cm and a -3.0 x 10^-9 C point charge is located at x=5.0cm. What is the magnitude of the force on the negatively charged object due to the presence of the positively charged object? Express the answer as a vector quantity using unit vector notation.

Here we compared the electrostatic force to the force of gravity and calculated a ratio between the two values.

Below is a picture of a Van de Graaff generator which is an electrostatic generator that using a moving belt to accumulate electric charge on the hollow metal sphere on top. 

Summary: 

• Electrostatic forces are the forces between particles that are not moving or are moving very slowly.
• Coulomb's Law is used to calculate the electrostatic force between two charge particles. 
• the direction of the forces are along the line between the two objects and is attractive if the particles have opposite signs and repulsive if they have the same signs
• the electric force originates from the charge on one particle and acts on the charge of another particle
• Van de Graaff generators are electrostatic generators that use moving belts to accumulate electric charge onto a hollow metal sphere connected on top.