Characteristics of Fluids
Fluids have several characteristics that define them as fluids. For example, fluids do not have a particular shape of their own. Instead, both gases and liquids take the shape of their container. Although liquids do not have a definite shape, they do have a definite volume, for example, if you pour 500 mL of a liquid from a tall, thin container into a short, wide container, its volume will still be 500 mL.
Gases, however, will fill any empty container they are placed
in. Imagine if a frightened skunk entered your classroom. Skunks can spray a very strong-smelling liquid to defend themselves. The liquid quickly evaporates into a gas. Although the spray itself may be only a few milliliters, the smell (which is caused by gas) quickly fills a room. Very soon, everyone in your school would know by the smell that a skunk is inside. Gases may not have a definite shape or volume, but some have a very
Solids have a definite shape and volume. Although the particles of a solid are in constant motion, the forces of attraction are so strong that the particles vibrate very small distances around a central point. The particles are more or less locked in place. They cannot slide past one another. This is why solids are generally not fluids.
Particles of liquids are farther apart than particles of solids. They are bound less tightly and are free to move past one another. The forces
of attraction among particles of liquids are still strong enough to hold the liquid together .
The particles of a gas are much farther apart, and their force of attraction is extremely small. Gas particles spread out and fill whatever container they are placed in.
The Particle Theory of Matter
The particle theory of matter helps explain why fluids act the way they do. It states that
- All matter is made of tiny particles
- Particles have empty spaces between them
- Particles are always moving
- Particles move faster and spread farther apart when they are heated
- Particles are always attracted to each other