Answer:
Many young students will have had memorable but often confusing experiences with magnets and magnetic materials. Magnetic materials are regularly encountered around the home, often holding small objects on the kitchen fridge or keeping cupboards and fridge doors closed. Many children’s toys employ weak magnets to ‘stick’ materials together (e.g. wooden train carriages) or are used in simple children’s construction toys to allow them to quickly assemble more complex structures without the need for messy adhesives or difficult connections. Toys very rarely make use of magnetic repulsion.
Many younger students are yet to form strong views or in many cases any views at all about how magnets interact with matter or each other. They do not see the need to discriminate between magnetic forces and electrostatic forces (or gravity). To them, these often appear to be common experiences of the same invisible non contact force, usually only attraction. For example, a balloon ‘rubbed’ with a cloth resulting in its attraction to another object is frequently described incorrectly by young students (and even some adults) as having been ‘magnetised’ in some way.
Students’ confusion around non contact forces is explored in the focus idea Electrostatics – Level 4.
It is well established that older students hold a range of views about magnetism that vary considerably in their sophistication, ranging from magnetic models with surrounding ‘clouds’ of action to ideas about ‘electric rays’ and ‘fields’. However, many younger students simply associate magnetism with a ‘pulling force’. Understandably their naive model has no predictive or explanatory power and they typically do not perceive the need to do more than identify and label the attractive or the less frequent repelling behaviour as magnetic.
Research: Erikson (1994), Borges & Gilbert (1998), Haupt (2006), Van Hook & Huziak-Clarke (2007), Ashbrook (2005), Hickey & Schibeci (1999), Maloney, O’Kuma, Heieggelke & Van Heuvelen (2001)
Scientific view
We frequently encounter magnetic fields in our everyday experiences (e.g. the Earth’s magnetic field and magnetic fields produced by electric current). However, the vast majority of the magnetic fields around us are simply too weak to cause any observed effects or remain ‘removed from us’ because they are utilised in more complex machines like electric motors and computer hard drives.
Magnetic attraction and repulsion is one of three fundamental non contact forces in nature. The other two forces are electrostatic and gravitational (see the focus idea Forces without contact at level 4, Electrostatics – Level 4 and Gravity - Level 6).
The vast majority of magnets we encounter (e.g. fridge magnets, door catches and magnetic toys) are manufactured from materials which are ferromagnetic. These materials are based on mixtures of iron, nickel or cobalt as these are the only three known ferromagnetic elements. Stronger industrial magnets can be made with these and the addition of more expensive rare earth elements.
The atoms in ferromagnetic materials are different because they can behave like little magnets. Normally the magnetic field around each atom points in a random direction resulting in them cancelling each other out (see Figure 1). However if the surrounding magnetic field is strong enough, it is possible for them to align so they each contribute to produce a stronger magnetic field in the material (see Figure 2). They can also remain aligned when the surrounding field is removed creating a permanent magnet.
Atomic fields
Typical magnets found around the house or used in guitar ‘pick ups’ or fish tank glass cleaners are constructed with ferromagnetic materials and can produce permanent magnetic fields with intensities up to 3000 times that of the Earth’s magnetic field.
Ferromagnetic materials are usually very brittle and will easily chip or fracture if dropped or allowed to slam together. They will also lose their permanent magnetic properties if heated strongly. All of these actions cause the individual atoms to lose their alignment.
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