Magnetic Interactions1
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One of the most basic and fundamental concepts in physics states that when two objects
touch, they interact by pushing or pulling on each other, such as when you
throw a ball or when you are sitting down. In each of these instances, the
motion of an object is influenced by the push or pull of another object
when in contact.
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However, can the motion of an object be influenced if it is not in physical
contact with any other object?
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In the following activities, we will investigate how magnetic objects
interact and hopefully gain some insight about how magnetic effects are
used in many different ways in the world around us – from holding notes
on your refrigerator, to recording information on computer disks or credit
cards (the magnetic strip on the back).
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Physical Sciences Connection: Forces and Motion; Types of Interactions (3-PS2-3)
Activity 1: Do magnets have to touch each other in order to interact?
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Initial thoughts: How can you tell if two magnets are interacting?
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Discuss your thoughts with your group.
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Part 1: Magnetic Interactions
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What you will need:
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• Two bar magnets (you may have to pair up with someone)
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Some of the material here is taken from Physics and Everyday thinking by Fred Goldberg.
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Take the two small magnets in your hands and bring their faces together slowly, but try not to let
them touch each other.
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Do the magnets exert a force on each other, even though they are not touching? How can you
tell?
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Does there seem to be a relationship between the strength of the magnetic force on each magnet
and how far apart the two magnets are? How do you know?
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Below, draw an arrow to show direction of the force on magnet A from magnet B.
Below, draw an arrow to show direction of the force on magnet B from magnet A.
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Now turn one of the magnets over and bring them together again.
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Do they behave in the same way as before, or does something different happen? If so, what?
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Do the magnets still exert a force on each other when they are not touching? If so, is there
anything different about the forces now
In this arrangement, does the strength of the magnetic force between the two magnets depend on
how far apart they are? If so, in what way?
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When two magnets either attract or repel each other in the way you have seen above, we call this
a magnetic interaction. The magnetic interaction is an example of what scientists call an
‘action-at-a-distance’ - this is an interaction in which objects can push or pull on each other
without touching. The most common example of this is gravity!
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How is it possible for two magnets to exert forces on each other without touching? Discuss with
your group and try to think of possible ideas to account for how this ‘action-at-a-distance’
occurs.
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The magnetic field
A magnetic field can be thought of as an invisible ‘field of influence’ around a magnet, an idea
that scientists find useful to account for the observation that magnetic interactions can occur
without physical contact.
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Part 2: What types of material interact with a magnet?
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What you will need:
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One bar magnet
Materials around the room
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Initial Thoughts:
What kinds of materials do you think would be attracted to a magnet? Be as specific as you can.
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Assuming these materials are not themselves magnets, do you think they can also be repelled
from a magnet?
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Using items around the room, determine whether the material is attracted to the magnet.
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Material
Attracted to the
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magnet?
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Choose an object made of a material that is attracted to the magnet. Turn the magnet around, so
its opposite pole faces the object.
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Is the object still attracted to the magnet?
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How is the interaction between a magnet and this object different from the interaction between
two magnets?
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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
or materials that include iron in them (like steel) are also ferromagnetic. (Nickel and cobalt are
also examples of ferromagnetic materials.)
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Summarizing Questions:
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An elementary school student asks you for advice about a project
she is doing on recycling. She suggests that a large magnet could
be used to separate metals from non-metals in the trash passing
through a recycling station. What do you think of this idea?
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