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Activity

Elastic and rigid properties of materials

Summary: 
Classify a collection of common materials by whether they deform and return to their original shape.
Science content (2016 curriculum): 
Chemistry: States of Matter, Properties of Materials (K-7)
Materials: 
  • worksheet, attached
  • collection of materials e.g. popsicle stick, metal strip, tin foil, pasta, rubber ball, ping pong ball, hard ball, foam, balloon, styrofoam, modelling clay, metal strip, rock, marble, silly putty (or students make it)
Procedure: 

Test the materials to determine how rigid, elastic and malleable they are. These are the properties of rigid, elastic and malleable materials:
Rigid materials do not deform easily.
Elastic materials can be deformed, then return to their original shape.
Malleable materials can be deformed, and do not return to their original shape.
(Note that technically, I should use the term "plastic" instead of malleable. But as the word plastic is used so often in another context, it would be confusing for students. Materials with plastic properties come in different types: malleable materials can be flattened easily, and ductile materials can be drawn into a long thread easily.)

The classification of the materials will depend on their thickness and shape, for example metal can be quite rigid if it is thick, or malleable if it is thin. Any answer is fine as long as the students are manipulating the materials and thinking about how they deform.
Our results: rigid materials were marble, rock, hard ball, bow tie pasta (spaghetti would be elastic too). Between rigid and elastic were metal strip, popsicle stick, plastic spoon, bouncy ball. Elastic materials were balloon, foam sponge. Between elastic and malleable were styrofoam and pipe cleaner. Malleable materials were play dough and tin foil. Between malleable and rigid is ping pong ball (though nearer rigid than on the photo).

If students are given several types of balls, ask them to see how elastic or rigid they feel, then based on that, predict how high they will bounce. The more elastic balls will generally bounce higher than more rigid balls. The elastic material stores energy as it is deformed, which is released again as it returns to its original shape, giving the ball energy to go higher.

At a molecular level, some of these properties can be explained.
Elastic materials are often made of long molecules that can bend and stretch, then return to their original shape e.g rubber. Elasticity may also be due to air pockets in the material that can be compressed e.g. foam.
Rigid materials will be made up of tightly-bonded molecules that are hard to move past each other. Sometimes rigid materials are brittle, so that with enough stress they break apart suddenly as the bonds are
Malleable silly putty has many weak bonds between long molecules that can be broken, then remade in new positions.

Attached documents: 
Grades taught: 
Gr 5
Teacher: 
Ingrid
Teaching site: 
ingridscience afterschool