Concrete is an example of a material that is strong in compression and weak in tension. This is why it is useful in walls, such as brick walls, where all the forces from the bricks, the upper floors and the roof act as compressive forces on the concrete bricks. Tension is a force that stretches something.oncrete is an example of a material that is strong in compression and weak in tension. This is why it is useful in walls, such as brick walls, where all the forces from the bricks, the upper floors and the roof act as compressive forces on the concrete bricks. Tension is a force that stretches something.
Rubidium is a chemical element with symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group, with an atomic mass of 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other alkali metals, such as very rapid oxidation in air.atural rubidium is a mix of two isotopes: 85 Rb, the only stable one, constitutes 72% of it. The remaining 28% is the slightly radioactive 87 Rb with a half-life of 49 billion yearsâmore than three times longer than the estimated age of the universe.
A very hard, brittle, silvery-white transition metal of the platinum group, iridium is generally credited with being the second densest element (after osmium) based on measured density, although calculations involving the space lattices of the elements show that iridium is denser.ridium in bulk metallic form is not biologically important or hazardous to health due to its lack of reactivity with tissues; there are only about 20 parts per trillion of iridium in human tissue. Like most metals, finely divided iridium powder can be hazardous to handle, as it is an irritant and may ignite in air.