Fluids and Particle Theory

Fluids do not have a fixed shape and yield to external pressure. Examples include water, honey, and juice.

Particle Theory

• Explains the behavior, changes, and interactions of matter.
• Helps in understanding fluids.

Postulates of the Particle Theory

• All matter consists of tiny particles.
• Particles have space between them.
• Particles are always in random motion.
• When heated, particles move faster and are further apart.
• Particles attract each other.

States of Matter

Liquids

• Particles are further apart compared to solids but still have some attraction, allowing them to flow.

Gases

• Particles are even further apart than in liquids.
• Gases have weaker forces of attraction.
• They flow like liquids but are less dense.

Solids

• Particles are closely packed with strong attraction, giving them definite shapes and volumes.
• Particles are locked in place and cannot flow, so they are not considered fluids.

Key Concepts in Fluids

Ability to Flow

• Fluids flow through, around, or over objects.
• Salt appears to flow, however each grain has a definite shape.

Buoyancy

• Fluids exert an upward force on an object, determining if it floats or sinks.

Buoyancy and Density

• Objects sink if their density is greater than the fluid.
• Objects float if their density is less than the fluid.
• Objects hover if their densities are equal.

Archimedes' Principle

• An object in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces.

Flow and Viscosity

Flow

• A fluid moves in a steady, continuous stream.
• Water flows faster than honey.

Flow Rate

• Represents the volume of fluid passing a point in a given time.
• If a 1L bottle fills in 4 seconds, the flow rate is 0.25L per second.

Viscosity

• The thickness or resistance of a fluid to flow.
• Caused by internal friction as particles rub against each other.
• More viscous fluids (like honey) flow slower.

Factors Affecting Viscosity

• Temperature: Heating fluids reduces viscosity and improves flow by making particles move faster.
• Cohesion: Attraction between particles of the same substance. honey has more of this, making it more viscous.
• Adhesion: the attraction between particles of fluids and other materials

Surface Tension

• The force of attraction between particles on a liquid's surface.
• Water striders can walk on water, as surface tension creates a "skin" on the surface.

Weight, Mass, Volume, and Density

Weight

• The force of gravity acting on an object.
• Weight varies depending on location (e.g., Earth vs. Moon).

Mass

• The amount of matter in an object or substance.
• Mass does not change regardless of location.

Volume

• The amount of space an object or substance occupies.
• Measured using tools like a graduated cylinder or by calculation.
• Common units are liters (L), milliliters (mL), and cubic units (m³, cm³).

Density

• Solids are more dense than liquids because their particles are closer together.
• Liquids are less dense than solids as their particles are further apart.
• Gases are much less dense than solids and liquids due to far-apart particles.
• Water is denser than oil, despite both being liquids, due to differences in particle arrangement.

Fluid Systems

• A group of parts functioning as a whole by interacting with at least one fluid.
• Fluid systems can be natural (e.g., movement of sea stars and the respiratory system) or manufactured.
• Pneumatic systems use compressed gas to transmit force, are safe, cost-effective, and reliable over a wide temperature range. An example is a drill.
• Hydraulic systems use liquids under pressure to transmit force and perform work.

Pumps & Valves

Valves

• Control the flow of fluids.
• A faucet is an example.

Pumps

• Move fluid into or through something.
• The heart pumps blood to the lungs and throughout the body.

Pascal's Law

• When force is applied to an enclosed fluid, the increase in pressure is transmitted equally throughout the fluid.
• Squeezing a stress ball or toothpaste tube demonstrates this law.

Types of Pressure

Atmospheric Pressure

• The force exerted by the weight of air on the Earth's surface, acting in all directions due to air molecule collisions.
• Higher altitude decreases the number of gas particles, resulting in less dense air and reduced atmospheric pressure.

Water Pressure

• Water exerts pressure in all directions, which is why water presses on the body when swimming underwater.
• Water exerts more pressure than air due to being heavier.

Fluid Chambers

• Pressure applied to one part of the fluid in a closed container is applied equally to all parts.
• When pushing on a small piston, the same force is applied throughout the fluid.
• A larger piston covers a bigger area and applies a much greater force.

Pressure

• The amount of force applied to a given area, increasing with depth.
• Fluids move from high to low pressure areas.
• Gases and liquids are fluids.

Changes in Pressure

• Air pressure changes altitude.
• Air pressure decreases with higher altitude, as gravity pulls air particles down.
• Pressure in a fluid increases with depth and is due to the weight of the fluid above.

Pressure & Fluid Flow

• Fluid always moves from high pressure to low pressure.
• When drinking through a straw, sucking reduces the pressure inside it, and higher outside pressure pushes the juice into the straw and mouth.

Pressure & Temperature

• Pressure in a fluid comes from particles pushing on things.
• Heating a fluid makes particles move faster.
• Faster particles hit the container walls harder, increasing pressure.

Compression

• When a force makes something smaller.
• Gases like air have lots of space between particles. Kicking a soccer ball forces air particles into less space.
• Liquids have less space between particles and so don't compress as easily.
• Gases compress more easily because their particles are farther apart.

Compressibility

• This is the ability to be squeezed or compressed.
• Liquids are incompressible, meaning they can't be easily squeezed.