11.1 What Is a Fluid?
2 min read•june 18, 2024
Matter exists in three main states: solid, liquid, and gas. Each state has unique properties based on how its particles are arranged and interact. Understanding these differences is key to grasping how materials behave in various situations.
, which include liquids and gases, flow and change shape easily. Solids, on the other hand, maintain a fixed shape. These behaviors stem from the molecular arrangements within each state, affecting how substances respond to forces and environmental changes.
Properties and Behavior of Matter
States of matter and properties
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- Solid
- Maintains definite shape and volume due to closely packed particles with fixed positions
- Particles vibrate in place but do not move freely (ice)
- Liquid
- Maintains definite volume but conforms to shape of container due to particles that are close together but can move around each other
- Flows and takes shape of container (water)
- Gas
- Lacks definite shape or volume and expands to fill container due to particles that are far apart and move randomly
- Compresses and expands easily (air)
Fluids vs solids behavior
- Fluids (liquids and gases) flow and change shape
- Particles in fluids move freely past one another allowing fluids to conform to shape of container (pouring water into a glass)
- Fluids can resist , which is a force applied parallel to a surface
- Solids maintain fixed shape and volume
- Particles in solids are fixed in position and cannot flow (a brick)
Molecular arrangement in fluids
- Liquids
- Molecules are close together but not as tightly packed as in solids resulting in a definite volume but no fixed shape
- are weaker than in solids allowing molecules to move past each other (liquid mercury)
- Nearly due to close proximity of molecules (trying to compress water)
- Gases
- Molecules are far apart and move randomly resulting in no definite shape or volume
- Negligible intermolecular forces allow gases to expand and compress easily (compressing air in a piston)
- Easily compressed because of large spaces between molecules (squeezing a balloon)
Fluid Behavior and Forces
- : The study of fluids at rest and the forces they exert
- : The study of fluids in motion and how they interact with their surroundings
- : The attraction between molecules of the same substance, contributing to in liquids
- : The attraction between molecules of different substances, influencing how fluids interact with surfaces
Key Terms to Review (22)
Adhesion: Adhesion is the phenomenon where two different surfaces or materials are held together by intermolecular forces, without the involvement of any intervening liquid. It is a fundamental concept that underpins various physical and biological processes, from the ability of geckos to climb walls to the cohesion of liquids and the function of biological membranes.
Archimedes: Archimedes was an ancient Greek mathematician, physicist, engineer, and inventor who lived in the 3rd century BC. He is best known for his contributions to the understanding of fluids and density, which are central to the topics of 11.1 What Is a Fluid? and 11.2 Density.
Archimedes’ principle: Archimedes’ principle states that a body immersed in a fluid experiences a buoyant force equal to the weight of the fluid displaced by the body. This principle explains why objects float or sink.
Buoyancy: Buoyancy is the upward force exerted by a fluid on an object immersed in it, which counteracts the object's weight and allows it to float or be suspended within the fluid. This concept is fundamental in understanding the behavior of objects in fluids and is closely related to the properties of fluids, density, pressure, and fluid dynamics.
Cohesion: Cohesion is the intermolecular force that causes like molecules to stick together, which is particularly significant in liquids. This property is crucial for understanding how fluids behave, including their ability to maintain shape and resist external forces. Cohesion plays a vital role in phenomena such as surface tension, where the cohesive forces at the surface of a liquid create a 'skin' effect, and is also essential in biological systems where it influences processes such as water transport in plants.
Compressibility: Compressibility is a measure of how much a fluid or material can be reduced in volume when subjected to an external pressure. It is a fundamental property that describes the ability of a substance to decrease in volume when a force is applied to it.
Critical density: Critical density is the theoretical density of matter needed for the universe to have a flat geometry. It determines whether the universe will expand forever, collapse back on itself, or reach a stable size.
Density: Density is a fundamental physical property that describes the mass per unit volume of a substance. It is a crucial concept in understanding the behavior of fluids and the principles governing various physical phenomena related to pressure, buoyancy, and fluid flow.
Fluid: A fluid is a substance that flows and takes the shape of the container it is in, unlike a solid which retains its own shape. Fluids can be liquids or gases, and they are characterized by their ability to deform under applied shear stress.
Fluid dynamics: Fluid dynamics is the branch of physics that studies the behavior of fluids (liquids and gases) in motion. It examines how forces affect the flow and movement of these substances, encompassing concepts like pressure, velocity, and viscosity, which are crucial in understanding phenomena in both natural and engineered systems.
Fluids: Fluids are substances that can flow and conform to the shape of their containers. They include both liquids and gases.
Hydrostatics: Hydrostatics is the study of fluids at rest and the pressures they exert. It encompasses the principles and laws that govern the behavior of stationary fluids, including their ability to transmit forces and create buoyancy.
Incompressible: Incompressible refers to a fluid that has a constant density, meaning it does not change in volume or density when pressure is applied. This property is significant when analyzing fluid behavior because it simplifies many calculations, allowing the assumption that the density of the fluid remains constant regardless of the pressure changes it may experience.
Intermolecular Forces: Intermolecular forces are the attractive or repulsive forces that exist between molecules, which determine the physical and chemical properties of substances. These forces play a crucial role in understanding the behavior of fluids, the surface tension and capillary action of liquids, as well as the phase changes that occur in matter.
Laminar Flow: Laminar flow is a type of fluid flow where the fluid travels in smooth, parallel layers with no disruption between the layers. It is characterized by a high degree of order and predictability in the fluid's movement.
Pascal's Principle: Pascal's principle states that in a fluid, pressure applied to any part of the fluid is transmitted equally to all parts of the fluid. This means that when a force is applied to a fluid, the pressure increases equally throughout the fluid, and this increased pressure is exerted on all surfaces in contact with the fluid.
Pressure Gradient: A pressure gradient is the change in pressure over a given distance within a fluid. It is a measure of the difference in pressure between two points and the direction in which the pressure is increasing or decreasing. The pressure gradient is an important concept in the study of fluid mechanics and is closely related to the movement and behavior of fluids.
Shear Stress: Shear stress is the component of stress coplanar with a material cross-section. It is the stress which acts tangentially to the face of the section. Shear stress is an important concept in the study of elasticity, fluid mechanics, and the motion of objects in viscous fluids.
Surface tension: Surface tension is the cohesive force at the surface of a liquid that makes it behave as an elastic sheet. It results from the greater attraction of liquid molecules to each other than to the molecules in the air.
Surface Tension: Surface tension is a property of liquids that arises from the cohesive forces between the molecules at the liquid's surface, causing the surface to behave like an elastic sheet. This property is crucial in understanding the behavior of fluids and the phenomena of capillary action and wetting.
Viscosity: Viscosity is a measure of a fluid's resistance to deformation or flow. It quantifies the internal friction within the fluid when it is in motion.
Viscosity: Viscosity is a measure of the resistance of a fluid to flow. It describes the internal friction within a fluid that causes it to resist motion and flow. Viscosity is a crucial property that affects the behavior of fluids in various contexts, including fluid dynamics, heat transfer, and transport processes.