Developing Our Ideas ACTIVITY: Experiments with Magnetism Purpose Magnets can also affect other objects that are not themselves magnets. The purpose of this activity is to investigate what kind of materials are affected by magnets, and to explore in greater depth some additional properties of the magnetic interaction. During the remainder of this Cycle you will use this information to construct a model to explain magnetism. What are some additional properties of the magnetic interaction? Initial Ideas What kinds of materials do you think would be attracted to a magnet? Be as specific as you can. Assuming these materials are not themselves magnets, can they also be repelled from a magnet? 2005 PET physics education for teachers by Fred Goldberg. This part of lab has been modified by Dr. Armen Kocharian in September 12, 2009. 4-1
Cycle 4 Collecting and Interpreting Evidence Experiment #1: What kinds of materials are attracted to a magnet? You will need: Magnet Set of different materials STEP 1. Take one item from the set of materials, and record its name in the Table. STEP 2. Determine whether the material is attracted to the magnet. Record your result in the Table. STEP 3. Repeat steps 1 and 2 for all the available materials. You may also check other materials you are curious about. Record your additional observations in the Table. Table: Observations with Magnet and Materials Material Is material attracted to a magnet? 4-2
Activity 1: Experiments with Magnetism STEP 4. Look over the data in your Table. Are all metals attracted to a magnet? What materials seem to be attracted to a magnet? Is there any evidence that a material that is attracted to a magnet, but is not itself a magnet, can also be repelled from a magnet? Scientists call materials that are attracted to a magnet, ferromagnetic materials. Magnets are also made of ferromagnetic materials. Iron is the most common ferromagnetic material, and objects that include iron in them (like steel) are ferromagnetic. (Nickel and cobalt are also examples of ferromagnetic materials.) For the remainder of this activity, you will use iron (or steel) nails to explore some important properties of the magnetic interaction. Experiment #2: What happens when a nail is rubbed with a magnet? Your group will need magnet three nails small Styrofoam float aluminum pie tin or Styrofoam plate glass beaker water In this experiment you will distinguish between two types of nails: those that are rubbed with a magnet (called rubbed), and those that are not rubbed with a magnet (called unrubbed). Note: Keep the magnets far away from the nails. Once you rub a nail, it is no longer unrubbed. Please do not rub the nails until you are asked to do so. 4-3
Cycle 4 STEP 1. Use the beaker to pour some water into the aluminum pie pan. Lay an unrubbed nail on a small, flat piece of Styrofoam and float it in the water. This will give a very sensitive test arrangement. Check that your aluminum pan is not sitting over a piece of metal under the table, and that there are no large metallic objects nearby. STEP 2. We first want you to investigate whether an unrubbed nail can affect another unrubbed nail. To determine this, take a second unrubbed nail, hold it horizontally, and bring its tip close to (but not touching) the floating nail. See picture to the right showing that the held nail should be at right angles to the floating nail. Always test held and floating nails this way. Do not bring the held nail from above (picture below to the left), nor bring it parallel to the floating nail (see picture below to the right). Do not do it this way Do not do it this way What, if anything, happens to the floating nail when the held unrubbed nail is brought nearby? 4-4
Activity 1: Experiments with Magnetism STEP 3. Make a rubbed nail as follows. Place one end of the bar magnet over one end of an unrubbed nail and rub in one direction only to the other end. Then lift the magnet away from the nail and repeat the process a few times, always rubbing in the same direction. STEP 4. Using the same procedure as described in step 2, bring the tip of a held rubbed nail near the tip of the floating unrubbed nail. What, if anything, happens to the tip of the floating unrubbed nail? STEP 5. Bring the tip of the held rubbed nail near the head of the floating unrubbed nail. What, if anything, happens to the head of the floating nail? STEP 6. Turn the held rubbed nail around and bring its head near the tip and head of the floating nail. Summarize what happens, if anything, to the tip and head of the floating unrubbed nail. STEP 7. Lay the rubbed nail aside for a moment. Imagine that you removed the floating nail, rubbed it with the magnet in the same way you rubbed the other nail, then floated it again. You would then have two rubbed nails one held and one floating. (Don t do it yet!) 4-5
Cycle 4 Predict what you think will happen if you were to bring the tip of the held rubbed nail near the tip of the floating rubbed nail. Predict what you think would happen if you were to bring the tip of the held rubbed nail hear the head of the floating rubbed nail? STEP 8. Now remove the floating nail, rub it with the magnet, and replace it on the floater. Then test your predictions. What actually happens when you bring the tip of the held rubbed nail near the tip of the floating rubbed nail? What actually happens when you bring the tip of the held rubbed nail near the head of the floating rubbed nail? STEP 9. Repeat step 8, but this time bring the head of the held rubbed nail near the tip and head of the floating rubbed nail. What happens? 4-6
Activity 1: Experiments with Magnetism Summarize your observations in this experiment by answering the following questions. What happens when the tip or head of an unrubbed nail is brought near the tip or head of another unrubbed nail? What happens when the tip or head of a rubbed nail is brought near the tip or head of an unrubbed nail? What happens when the tip or head of a rubbed nail is brought near the tip or head of another rubbed nail? Based on your observations, would you claim that a rubbed nail behaves like a magnet or like a ferromagnetic material that is not itself a magnet? What is your evidence? Discuss your answer to this question with at least one other group. Add any additional comments below. 4-7
Cycle 4 Experiment #3: Does a rubbed nail interact with anything when there is no other magnet or nail nearby? In the previous experiment you observed what happens when a rubbed nail is brought near an unrubbed nail or another rubbed nail. One of the things you probably discovered was that a rubbed nail behaves like a magnet. Consider floating a rubbed nail. If you do not bring another nail or magnet nearby, does anything interesting happen to the floating rubbed nail? You will answer that question in this experiment. STEP 1. Place a rubbed nail on the floater, making sure the other rubbed nail and magnet are far away. Spin the floating rubbed nail gently, and watch it. You should watch the nail for at least half a minute. Repeat this several times. Does the floating rubbed nail generally point in different directions after each spin, or does it always seem to end up pointing in the same direction? STEP 2. Try aiming the floating rubbed nail in different directions, then letting go so it settles into a position. You may have to wait as long as one minute to be sure of what you are seeing. What does the nail do? STEP 3. Compare your observations with that of several (at least five) other groups. What is the same (if anything)? What is different (if anything)? 4-8
Activity 1: Experiments with Magnetism Experiment #4: How can you rub the nail so it consistently behaves a particular way? In the previous experiment you probably discovered that when some groups floated their rubbed nail and let it settle, the pointed end ended up pointing towards the geographical north. For other groups, the head end of their rubbed nails ended up pointing towards the geographical north. Whenever a rubbed nail, or any magnet, is allowed to rotate freely, and without another magnet nearby, one end will always end up pointing (approximately) towards the geographical north pole of the Earth. By mutual agreement, scientists define this end of the magnet as the north pole of the magnet. The opposite end of the magnet, by definition, is called the south pole. Thus, when you rub your nail you produce a magnet with a north pole and a south pole. STEP 1. Figure out two different ways that you can rub your nail with a magnet so that the pointed end becomes the north pole and the head end becomes the south pole. Draw some sketches showing how you did it. Also describe what you did in words. 4-9
Cycle 4 STEP 2. Figure out two different ways that you can rub your nail with a magnet so that the head end becomes the north pole and the pointed end becomes the south pole. Draw some sketches and describe in words how you did it. Summarizing Questions S1. Do both ends of a rubbed nail (magnet) behave similarly or differently when interacting with another rubbed nail? How do you know? S2. In what ways does a rubbed nail seem to be different from an unrubbed nail when interacting with another rubbed nail? Participate in a whole class discussion to review the results of the experiments and the answers to the Summarizing questions. 4-10