Definitions of some properties words:

The true definition of strength is in connection with how much force is required to stretch and pull apart a material. An elastic material increases in length when a force is applied but returns to its original length when the force is removed. A plastic material stretches when sufficient force is applied but does not return to its original length when the force is removed. The word plastic is commonly used as the name for a material type but here it is being used as an adjective to describe a property of a material.

Shiny materials reflect light from their surface. Metals are shiny but may be a variety of colours eg. gold, copper is orange/brown, brass is similar to gold, silver. The shiny appearance of a metal is often called ‘lustre’.

A hard material resists being scratched on the surface by other materials. Hardness and strength are not the same. Diamond is harder than glass and can scratch it easily. A diamond tipped cutter is used to draw lines on glass in order to cut or break it cleanly.

Conductor of heat
A good conductor of heat allows heat energy to travel through it quickly. Heat travels from a place of high temperature to a place of low temperature. A good insulator is the opposite of a good conductor and prevents heat from traveling as quickly. It can cause confusion when we think of good insulators as being the same as bad conductors. Good conductors of heat feel cold to the touch because they quickly conduct the heat away from our fingers and leave us with a cold sensation on our skin. Wood, plastics and fabrics feel mildly warm to the touch because they are good insulators and prevent our fingers from losing heat into the air as normal. Our skin cells warm a little because they can no longer get rid of heat and so we feel a warm sensation.

Heaviness and lightness are difficult concepts for young children because two things have to be considered at the same time when making a judgement. The mass of the material and the size! It is always best to compare the mass of equal size pieces of material so that a fair comparison is being made. By ‘heavy’ we often really mean high density and that a small amount of the material weighs more than we might expect. By ‘light’ we often mean ‘low density’ and that even a lot of it doesn’t weigh very much. Comparing the mass of equal size pieces of wood, plastic, steel and aluminium is a really worthwhile exercise.


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