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Name: Ms. Johnson
Status: Educator
Grade: K-3
Location: IL
Country: USA
Date: November 2005


Question:
One of my first grade students wants to be a builder when he grows up and he wants to "What is the name of the strongest kind of mixed metals?" He says that it will be a "sandwich with the metal as the bread and diamonds as the inside and the main base will be in Lake Michigan. It will be underwater and and above water." My student's name is Alex and you can email me with the answer.



Replies:
Very incisive suggestion by a K-3 student. There is a basic problem with defining the word "strong", because it has several meanings. It is sometimes used in the sense of a "hard" material. A material like diamond or even common glass is "strong" in the sense of hard, but these examples also tend to be "brittle", in common terms they do not have any "give", so when they are distorted in some way they do not "adapt" and "shatter" as a result. At the other extreme, there are materials like taffy or chewing gum that just stretch and stretch and stretch many times their initial size, but they are "soft", even "gooey", but in a sense they are strong because they do not "break" easily. In between, are materials like leather that are "strong" because they are "tough", that is they "give" or "adapt" a little when distorted but resist forces such as tearing.

From an engineering point of view, the student is on the right path. Strong materials are often composites of two or more components. One component providing "hardness", another component providing some "give" or elasticity so that forces applied to the material can be spread out and do not all come together at a point. It is a bit more complicated though, because the two materials must stick to one another so that they are in mechanical contact.

An automobile tire is a good example of a composite that uses these various factors: The rubber provides "give" or elasticity, the carbon black (though not very hard) provides a solid phase so that the tire is not "sticky", and the tire tread (bands of metal or some sort of woven fiber) provides a way for any stress on the tire at one point to be spread out over the whole tire, thus "diluting" the applied stress.

All of these come into play. But there is also the cost factor. I think a diamond-based material would be very expensive. I think the student could do a "Google" search on terms such as "strong materials", "strong construction materials", or similar terms and find age-appropriate sites that would give him some even different ideas.

Vince Calder



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