The Research Experience for Teachers Program /
http://www.cs.appstate.edu/ret
Subject Area(s): Physics
Computer Science Tools: Movie Maker, Image J, Excel
Activity Title: “Investigating Coulomb’s Law using Image Processing ”
Grade Level: 11-12
Time Required: 90 minutes
Recommended Group Size: 3 students
Summary: In this activity, students will use Movie Maker to record two similar-charged objects approach each other. Then students will use ImageJ to determine distances between the objects and estimate how far one object has been displaced as a result of the electrostatic force from the other. From the data students will gather the inverse square law should be determined.
Computer Science Connection: Students will develop the inverse square law using the data they will obtain from the videos of the experiment in Movie Maker and ImageJ. Computer scientists often have to gather data from images and then use them to find specific relationships.
Keywords: Electrostatics, Coulomb’s Law, Physics, ImageJ, Movie Maker
Educational Standards:
Pre-Requisite Knowledge: Students should have experience working with Movie Maker, Image J, and Microsoft Excel software. Students should have already been introduced to and have had experience with how charged objects behave around other charged objects. They also need to know how they can charge objects with electrostatic charge.
Learning Objectives: Students will be able to:
· Use Movie Maker and Image J to gather data
· Analyze data
· Draw conclusions from data and graphs
· Determine the relationship between the distance between two charged objects and the force between those objects.
Materials List:
· Static electricity equipment (balloons, pith balls, PVC pipes-small size, fur)
· Digital camcorder/tripod
· A Meter-stick
· ImageJ and Microsoft Movie Make software
Introduction/Motivation: Static electricity principles are used throughout industry and have to be managed in many different devices-including the computer! An understanding of the fundamental principles will help students in many different situations.
Engineer guy explains how a photocopier works
http://www.engineerguy.com/videos/video-copier.htm
More industrial uses of static electricity
http://www.school-for-champions.com/science/static_uses.htm
Background: Coulombs Law states that the force experienced between two charged objects is directly related to the product of the charge on the objects and inversely related to the square of the distance of separation between the objects. In this lab we are trying to discover the inverse square aspect of this relationship. In an equation Coulombs Law is written as:
F = kq1q2d2 or F = 14πεo q1q2d2;
where k and eo are fundamental constants.
Because of the difficultly of measuring the amount of charge on an object we will not be able to determine these values but you can make sure that these values stays constant through the use of Movie Maker. By recording the charged objects approaching each other, we can assume these values do not change.
To get a value for the force we will measure how far the hanging object is displaced from its initial position. The amount that this object is moved is proportional to the applied force acting upon it. You could discuss a person acting on a child in a swing. The larger the applied force the more the child is displaced from their rest position.
Preparation: To help complete this lab in 90 minutes the teacher should go ahead and make some videos of two charged objects approaching each other. This allows the students to quickly pick a video to analyze. You will need to decide how to share the videos with the students depending on your school’s network.
Some hints on making the videos:
· Make sure there is plenty of light-easier to see the objects.
· Have a white board in the background-easier to see the objects.
· Make sure the camcorder is at the same height as the suspended object and perpendicular to the two objects. Parallax can have a huge impact on the results of this lab.
· The suspended object needs to be hung from two strings so that it cannot move toward or away from the camera. See Figure 1
Figure 1
· Try to make sure you bring the other object directly at the suspended object at a constant rate-not too fast!
· If the students get good results from one particular video make sure to save it for next year!
Pre-Assessment
· Have students describe how charged objects interact around other charged objects.
· Have students explain how objects can become charged.
· Have students predict how the interaction between two charged objects will change when the objects are twice as far away from each other? Half the distance? Quarter of the distance?
Reference(s)
http://www.school-for-champions.com/default.htm
http://www.engineerguy.com/index.htm