Fluids Science Notes - PDF

Science Notes - Fluids (Unit 2) Fluids What Are Fluids? ​ Any substance that doesn’t have a fixed shape and gives in to external pressure easily. ○​ Examples: Water, honey, juice, etc. The Particle Theory ​ Explains how matter behaves, how it changes, and...

Science Notes - Fluids (Unit 2) Fluids What Are Fluids? ​ Any substance that doesn’t have a fixed shape and gives in to external pressure easily. ○​ Examples: Water, honey, juice, etc. The Particle Theory ​ Explains how matter behaves, how it changes, and how it interacts. ​ It helps us understand why fluids act the way they do. The 5 Postulates of the Particle Theory : 1.​ All matter is made up of tiny particles. 2.​ Particles have space between them. 3.​ Particles are randomly moving at all times. 4.​ When heated, particles move faster and further apart. 5.​ Particles attract each other. States of Matter Liquids ​ Particles are further apart than solids, but still have some attraction, allowing them to flow. Gases ​ Particles are even further apart than liquids, with weaker forces of attraction. ○​ Gases flow like liquids but are less dense. Solids ​ Particles are closely packed and have strong attraction , so solids have definite shapes and volumes. ○​ Particles are locked in place and cannot flow, so they aren't considered fluids. Key Concepts in Fluids The Ability to Flow ​ Fluidscan flow through, around, or over objects. ○​ Example: Salt appears to flow but each grain has a definite shape. Buoyancy ​ The upward force that a fluid exerts on an object, determining whether it will float or sink. ○​ Buoyancy and Density: ​ If the density of the object is greater than the fluid, it sinks. ​ If the density of the object is less than the fluid, it floats. ​ If the densities are equal, the object will hover. Archimedes' Principle ​ Discovered that an object in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces. Flow and Viscosity Flow ​ The movement of a fluid in a steady, continuous stream. ○​ Example: Water flows faster than honey. Flow Rate ​ The volume of fluid passing a point in a given time. ○​ Example: If it takes 4 seconds to fill a 1L bottle, the flow rate is 1L / 4 seconds = 0.25L per second. Viscosity ​ The thickness or resistance to flow in a fluid. ○​ Cause: Internal friction as particles rub against each other. ○​ Effect: More viscous fluids (like honey) flow slower. Factors Affecting Viscosity: 1.​ Temperature: Heating a fluid makes particles move faster, reducing viscosity and improving flow. 2.​ Cohesion: Attraction between particles of the same substance (e.g., honey has more cohesion, making it more viscous). 3.​ Adhesion: Attraction between the fluid particles and other materials (e.g., juice sticking to the sides of a glass). Surface Tension ​ The force of attraction between particles on the surface of a liquid. ○​ Example: Water striders can walk on water because surface tension creates a "skin" on the surface. Weight, Mass, Volume, and Density Weight ​ The force of gravity acting on an object. ○​ Varies depending on location (e.g., Earth vs. Moon). Mass ​ The amount of matter in an object or substance. ○​ Does not change regardless of location. Key Example : ​ On the Moon, your weight decreases due to weaker gravity, but your mass remains the same. Volume ​ The amount of space an object or substance occupies. ○​ Measured with tools like a graduated cylinder or calculated using dimensions. ○​ Common units: liters (L), milliliters (mL), cubic units (m³, cm³). Density ​ are more dense than liquids due to particles being closer Solids together. ​ Liquids have particles further apart, making them less dense than solids. ​ Gases have far-apart particles, making them much less dense than solids and liquids. Example : ​ Water is denser than oil, even though both are liquids, due to differences in their particle arrangement. What are Fluid Systems? A fluid system is a group of parts that function as a whole by interacting with each other and include at least one fluid. Fluid Systems can be natural ( e.g. movement of seas stars and the respiratory system) and/or manufactured. Examples: ​ Pneumatic systems  -​ Uses gas under pressure to transmit a force. -​ Gases must be compressed before being put into work. -​ Safe, have a reasonable cost, and are more reliable over a larger temperature. -​ An example would be a drill. ​ Hydraulic systems -​ Use liquids under pressure to transmit a force and do work. -​ Most machines used by construction workers could be some examples. Pumps & Valves ​ Valves -​ Devices that control the flow of fluids -​ E.x. When using a faucet, turning the tap one way allows water to flow out whereas turning it the other way stops the flow of water. ​ Pumps -​ Devices that move fluid into or through something. -​ E.x. A heart pumps blood into the lungs for oxygen, then pumps the blood throughout our bodies. —---------------------------------------------------------------------------------------------- Pascal’s Law Pascal’s Law: Pascal’s law states that when force is applied to an enclosed fluid, the increase in pressure is transmitted equally to all parts of the fluid (e.g Squeezing a stress ball and squeezing toothpaste out of its tube) —----------------------------------------------------------------------------------------------------- Types of Pressure ​ Atmospheric pressure -​ The force exerted by the weight of the air on the Earth’s surface acts in all directions due to the collision of air molecules.  -​ - the number of gas particles in the air Altitude increases (atmospheric pressure) decreases -​ Air becomes less dense due to fewer molecules being available to exert pressure. ​ Water pressure -​ Water also exerts pressure in all directions, for example when you swim underwater, water presses on your body. -​ Water exerts more pressure than air due to water being heavier than air. —---------------------------------------------------------------------------------------------------- Fluid Chambers ​ In a closed container, when there is pressure applied to one part of the fluid, it will be applied to all parts equally. ​ When pushing on the small piston, the same force will be applied equally throughout the fluid. ​ A larger piston covers a much bigger area, meaning the force it applies is much greater than the smaller piston. —---------------------------------------------------------------------------------------------------- Pressure Pressure is the amount of force applied to a given area, and it increases with depth. ​ Fluids will move from an area of high pressure to an area of lower pressure. ​ All gases and liquids count as fluids meaning that air is a fluid and exerts pressure around us all the time. Changes in Pressure ​ Air pressure changes altitude -​ For example, Air pressure is caused by gravity pulling air particles down. It decreases with higher altitude. —----------------------------------------------------------------------------------------------------- Pressure & Depth ​ Pressure in a fluid increases with depth. ​ The weight of the fluid above pushes down on the fluid below. ​ In a swimming pool, the deeper you go, the greater the pressure. Pressure & Fluid Flow ​ Fluid always moves from high pressure to low pressure. -​ For example when drinking through a straw. When you suck on a straw, you reduce the pressure inside it. -​ The higher pressure outside pushes the juice into the straw and your mouth. Pressure & Temperature What happens to pressure inside a container when the temperature of a fluid is increased? ​ The pressure in a fluid comes from all the particles pushing on things. ​ When you heat a fluid, the particles move faster. -​ Faster particles hit the walls of the container more and harder, this makes the pressure go up —----------------------------------------------------------------------------------------------------- Compression ​ Compression is when a force makes something smaller. ​ Gases, like the air in a soccer ball, have lots of space between particles. -​ Kicking the ball forces the air particles into a smaller space. ​ Liquids have less space between particles, so they don’t compress as easily. ​ Gases can be squeezed much more than liquids because the particles are farther apart. Compressibility ​ Compressibility is the ability to be squeezed or compressed. ​ Liquids are incompressible, meaning they can't be squeezed easily.