Day 1: Gaining Familiarity
Student Pages

Organizing Questions:

• What is a magnet?
• How does it work?
• Who first discovered magnetism?
• Are you near or in a magnetic object right now? How do you know?

Background information:

Check the following Web pages for information about magnetism and its history. Your teacher may have other web pages for you to look at or a reading assignment also.

• A brief introduction to magnetism written by a student:
  http://gamma.mhpcc.edu/schools/hoala/magnets/magnet.htm
• A brief discussion of the history of Western understanding of magnetism (and electricity) see Michael Fowler's essay at:
  http://galileoandeinstein.physics.virginia.edu/more_stuff/E&M_Hist.html
• A time line which includes non-Western knowledge of magnetism (and electricity and optics, closely related topics):
  http://history.hyperjeff.net/electromagnetism.html
• Two sources on Magnetic Levitation:
  http://www.dmoz.org/Science/Physics/Electromagnetism/Magnetic_Levitation/
  http://www.calpoly.edu/~cm/studpage/clottich/fund.html
• Motion of a charged particle in a magnetic field:
  http://www3.adnc.com/~topquark/fun/JAVA/electmag/electmag.html

Magnetism is a pretty mysterious thing. We often call it magnetism when a particular kind of object will attach itself to another similar object or some metals without glue or tape. Two such objects can also repel or force each other apart.

In this activity, you will:

1. Observe attraction and repulsion.
2. Develop a convention for saying what direction the force of a magnet is acting.
3. Observe the difficulty of using permanent magnets to levitate an object.
4. Qualitatively determine a force -separation relationship.
5. Observe interactions with non-magnetic materials.
6. Observe the relationship between the mass and strength of a magnet.

Your job is to make careful observations and record them in your notebook. Pick-up the set of items to work with from your teacher. You will use the pendulum to measure qualitatively the strength of the effect of one magnet on another with and without intervening materials.

Procedure:

1. Set-up pendulum with one of the provided magnets as the pendulum mass as shown in the figure.
   1. Using other magnets, cause the pendulum to be displaced, first through attraction and then through repulsion. Why is it so hard to hold the pendulum steady when it is displaced?
   2. Can you determine, simply by looking at magnets, which ends will be attractive or repulsive? Develop (and be able to explain) a system of labeling the magnets so that you can easily and reliably predict what will happen when it comes near another labeled magnet. Label your magnets.
   3. One at a time bring materials that are not magnets close to the pendulum. Observe and record the effect of the material on the pendulum. Is the pendulum attracted or repelled by the material? Does it matter if the material carries a static electric charge? Does it matter if the material is moving? What materials seem most likely to cause a magnet to be displaced? Explain your answer!
   4. Use one magnet to displace the pendulum and pass other materials between the two magnets. Which materials cause the displacement to change even though you did not move the magnets? Does it matter if you shake or move the material?
   5. Working with the magnet on the pendulum, can you find a way to screen it or otherwise hide it from another magnet? That is, construct some kind of barrier through which one magnet cannot affect another. Explain how it works.
2. Using 5 or more bar and other magnets, create a closed irregular polygon shape. Stand a small bar magnet on end in the interior portion. By small, we mean that the standing bar magnet should be shorter than the shortest side of the polygon. Find the locations inside the polygon at which the bar magnet will remain where you place it on end. Explain why these locations do not have to be at the geometric center of the polygon or at the centroid of the figure or at the center of mass of the polygon system. Why should you be careful not to do this on a metal table? Is the mass of a magnet related to the magnetic force it creates?
3. Using a pencil, several ring magnets, a ruler, and washers of known mass, gather data that lets you plot the relationship between the mass of washers supported on the upper magnet (vertical axis) and the separation (horizontal axis) between the two magnets. The image shows the set-up for data collection. Does this graph suggest a particular force-separation dependence? Characterize the dependence in words. What is the force equivalent of a washer (mass times acceleration due to gravity)? Repeat with different numbers of magnets in each stack and decide if the force-separation graph changes in a reasonable way (Is it simply displaced on one or both axis or is it a different character relationship?)
4. Using the copper tube in a vertical orientation, drop a magnet into it. Drop a piece of chalk into the tube. What happens to the motion of the magnet while it is in the tube that is different than what happened with the chalk? Write down likely causes of the observed behavior. Does the same thing happen if you drop a magnet just outside the tube? Explain what evidence you used to answer the questions and what it tells you about the nature of magnets. Based on your experience with attracting and repelling magnets, draw a diagram of the forces on the magnet inside the tube.
   Repeat with the plastic tube. What is different about the chemical structure of the molecules making up the plastic tube as compared to the molecules in the copper tube? Which of the differences contribute to the behavior of a magnet falling through a copper and a plastic tube? How and why?
5. Cause a metal paperclip to become magnetic. That is, verify that a paperclip is not magnetic, and then find a way to make it magnetic. Show the paper clip is magnetic by using it to pick-up an unmagnetized paper clip. Explain what is changed about the paper clip that makes it become magnetic.

After completing the observations, we will discuss our results. Before the discussion starts, write down any general conclusions about magnets that your observations seem to point toward.

Suggested Homework:

1. Write down a question you have about magnets and their interaction with each other. Design a means of testing magnetic interactions for information that helps you answer your question. Design a method for detecting a magnetic field. Explain how the detection method must rely on Newton's Third Law.
2. We know both gravitational and electric forces change strength as you move closer or farther from the source. Design a method to test for such a dependence with magnets.
3. Use Newton's Law to calculate the magnetic force of interaction on a magnetic pendulum in the vicinity of a 2nd magnet. The students cannot assume the magnetic force is completely horizontal. The following free body diagram is suggested:
   
   The smallest angle of B with the horizontal is gamma. The larger angle of T with the horizontal is theta. The weight (mg) is along the downward vertical. Find B(gamma,theta,W). Solve for the three cases gamma = 0°, gamma = 90°, gamma = theta.

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Lesson Development/Writing: Ed Eckel
Web Design: Theresa Valentine
Last Updated: 8/15/2000