Solids
Solids are very uniform. They have a definite shape and a definite volume. Scientists usually describe solids as being crystalline or amorphous. Crystalline means that the molecules have a pattern. Amorphous means they are placed randomly.
All the little molecules of matter are always moving, but they manage to keep their form. If you could zoom in and see the molecules in the mouse in your hand, you would see these tiny particles speeding around all over the place. If two were to collide they would bounce off of each other like rubber balls. That's basically what the the Kinetic Theory of Matter states: all molecules are moving and all collisions are elastic.
Now you may be thinking if their moving and bouncing all over the place, why don't they just break apart and fly away? Good question. Here's the reason: forces of attraction. There are forces in crystals called van de Waals forces. They were named after a Dutch scientist, Johannes Diderik van de Waals. They hold the particles in a definite shape. The general term for the force of attraction between like molecules is called cohesion.
If a solid is broken, a layer of gas molecules quickly cling to the broken surface so no atoms can spill out. The gas also stops the pieces from being perfectly rejoined. With some surfaces, if you polish them very well, and slide them together, cohesion will make them stick.
Molecules that are unlike are attracted to each other sometimes, too. Water wets glass and glue sticks to almost everything. The force of attraction between different molecules is called adhesion. That's why glue is called an adhesive. For a more in-depth explanation of cohesion and adhesion, visit our Liquids page.
Solids can be described in many ways. Metals are said to be ductile and malleable. Rubber balls have elasticity. No matter how you describe it matter is all around us, and in many different forms. So next time someone says to you "What's the matter?" You can tell them "Everything!"
