2 Material Property Station
Crystals
A crystal is a solid with flat sides and a symmetrical shape because its molecules are arranged in a unique, repeating pattern. A simple way to show what a crystal may look like is by using a model. A model is a representation of something. The particular type of crystal that forms depends primarily on the nature of the substance. Other factors, such as the temperature at which the crystallization takes place can influence the structure also. Table salt, for example, has a cubic crystal structure. Sugar has a hexagonal crystal structure. Borax can also be distinguished from the other substances by its crystal structure. Ideal crystal formation takes place over a relatively long time period (often many days or longer).
Sugar Crystals
Borax Crystal Shape Salt Model
Material Property Station
Heat
Thermal energy is required in many different aspects of our lives. This transfer of energy can occur by three methods: conduction, convection or radiation. Conduction is the most direct transfer of energy, as it requires two objects to directly contact one another. Thermal energy moves from particle to particle throughout a material as heat is conducted.
The mechanism of conduction is simple. As the temperature of a substance increases, so does the kinetic energy of its individual particles, which causes them to resonate rapidly within that substance. These high energy particles then collide with those at a lower temperature, transferring energy through the substance. For example, if a metallic spoon were placed in hot water, initially only the particles in contact with the water would increase in thermal energy. The energy would then propagate through the spoon until heat was felt at its handle. When a gas such as air is bumped by a fast moving piston, energy is transferred in the form of heat to the particles. The compression in the pump forces the particles of air closer together, increasing the number of collisions that propagate the heat.
Some materials are naturally good conductors of heat, while others are poor. Metals usually conduct heat extremely well, which explains the use of iron and copper in cooking utensils. Materials such as plastic, glass or wood do not conduct well.
Material Property Station
States of Matter
Gases, liquids and solids are all made up of microscopic particles, but the behaviors of these particles differ in the three phases. The following figure illustrates the microscopic differences.
Microscopic view of a gas. / Microscopic view of a liquid. / Microscopic view of a solid.Note that:
- Particles in a:
- gas are well separated with no regular arrangement.
- liquid are close together with no regular arrangement.
- solid are tightly packed, usually in a regular pattern.
- Particles in a:
- gas vibrate and move freely at high speeds.
- liquid vibrate, move about, and slide past each other.
- solid vibrate (jiggle) but generally do not move from place to place.
Material Property Station
Density
Solids which are more dense than a liquid will sink in that liquid, and solids which are less dense than a liquid will float on that liquid. Many metal items, like coins, will sink in water. However, a metal boat will float. Since density=mass/volume, increasing the volume of an object made of metal decreases the density of the object. Once the volume is increased so much that the density of the object is less than the density of water, the metal object will float. It is important to remember that forming the metal into a boat shape changes the density of the boat, however, the density of the metal itself cannot be changed. It is also important to remember that as cargo is loaded onto the boat, the mass of the “object” increases causing the density to increase as well. When the average density of the boat increases above that of the water, the boat sinks!