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Let's use a nail to test the hardness of some everyday objects. Before each scratch test, try to predict the result!
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Strength, Hardness and Flexibility
People sometimes think that strength and hardness are the same property. Although hard objects can be strong and strong objects can be hard, they are different properties.

Strength is the ability of a material to retain its structure when forces are applied to it. There are two main types of strength – compressive strength and tensile strength.

Compressive strength is a measure of how much a material can be pressed together before breaking. Materials such as steel, rocks, glass, concrete and some ceramics have high compressive strength.

Tensile strength is a material’s ability to withstand being pulled apart without stretching or breaking. Steel, bamboo and carbon fiber have high tensile strength.

Graphene is a transparent material made of a single layer of carbon atoms arranged in a honeycomb-like pattern. It is the world’s strongest material and also the most conductive in terms of heat and electricity.

Hardness is the ability of a material to withstand being scratched or indented. To determine the hardness of a material, you can scratch it with other materials of known hardness or measure the amount of force required to indent it. Generally, harder materials are more difficult to cut than softer materials. Diamond, steel, granite and concrete are hard materials.

Flexibility is how much a material can be bent or stretched without breaking. Rubber, plastics and fabrics are often made to be flexible.