The majority of the foods the students come in contact with appear as a solid, such as hamburgers and grains of cereal. The students need to understand how solids behave in order to describe the changes they see happening. Solids are distinguishable because all solids have a definite shape, which is not easily changeable. A solid can easily be picked up, pushed on, turned around and still its shape will stay the same.
The molecules in a solid are packed tightly together and cannot move around easily, thus preventing them from moving far apart. The molecules within a solid have a stronger attraction to one another than those in a liquid or a gas. The molecules in a solid are very compact or dense. Density is a term used for how tightly packed the molecules with in a solid are. Solids tend to be the densest of all three phases of matter. This is the reason why solids have a consistent shape.
A solid will expand as it is heated, because the atoms within it will vibrate vigorously.
This vibration allows the bonds to stretch and spread apart. The molecules will have more mobility and freedom to move about instead of staying together. As a solid is heated at a high enough temperature it will melt and will enter the liquid state. The solid has reached its melting point and is now starting to transform into a liquid.