Fluids A fluid is a substance that has

Fluids A fluid is a substance that has: • no defined form(takes shape of container) • can flow in all directions. • ALL LIQUIDS AND GASES ARE FLUIDS! • The body is full of fluids - liquids and gases!! • Blood=liquid Air = gas Refer to pages 66 & 67:

• Exception: Powders such as flour or sand are not considered fluids even though they have no form and flow. They are composed of small particles with a definite form.

Fluids and Particle Model of Matter (Review) • Gases: (oxygen, smoke, carbon dioxide) particles of a gas are far apart from one another and bound together by weaker forces of attraction. The gas particles can slide over each other in all directions and take shape of any container. • Liquids: (water) liquid particles are a bit closer together and bound together by weak forces of attraction. • Solids: (sand). Although these look like they can be a fluid because they move, each grain has it’s own particles that are bound by strong forces of attraction, so it will form piles. Solids are NOT fluids.

Determining if a substance is a fluid • It can sometimes be difficult to determine if a substance is a fluid or not • Here are some particular cases • Some substances are mixtures in a liquid or gaseous phase that contains solid particles. Since these substances are still capable of flowing they are considered fluids • Other substances like gels or pastes are harder to identify… what do you think? • If they can flow and take on the form of their containers, they are FLUIDS! *** Toothpaste not a fluid

Properties of Fluids • Viscosity: the ability of a liquid to flow • Honey: high viscosity • Water: low viscosity • Density: the relationship between a fluids mass and volume (mass/ volume) • These properties vary between fluids.

2 Types of Fluids Compressible and Incompressible Fluids are compressible if their volume can be reduce by exerting a force on the fluid. Gases (air) are compressible because their particles are further apart. When compressed, their particles will move closer together and reorganize to take up the remaining space. (Increased pressure=decreased volume) Ex: air, propane tank

• Fluids are incompressible if their volume cannot be changed or varied by an exerting force. Instead of change in volume there is a transmission of force from one particle to another. Liquids (water) are incompressible. When compressed, their volume will not decrease because their particles are already closer together and cannot be condensed. Take shape of container. • Ex: Blood: forced through vessels by heart pumping

Pressure • Pressure is the measurement of force applied to a surface. • When we push on something, we apply a force on it. • If that force is large enough it will move or deform the object. • Force: action that modifies than change the movement of an object or causes the shape of the object to change • When we apply a force on a fluid, the fluid exerts a force on the container holding it.

Relationship between Pressure and applied Force : • As the force increases, pressure increases • As the force decreases, pressure decreases Ex: Water exerts force. When a person dives under water, the water column above them pushes down on them, more pressure is exerted. You can feel this on eardrums. The deeper you dive, the more pressure on ears drums (pain)-more depth and you can rupture them. **pressure is directly proportional to the force applied Press ure (N/m 3) Ex: page 71 Force (N)

Relationship between Pressure and Area: • The greater the area that force is exerted over, the lower the pressure. (snowshoes on snow, surface area is bigger, so pressure is spread out) • Less area that force is exposed to , pressure increases. (boots on snow, surface area is smaller, so pressure is concentrated to one place) By changing the area the force is acting on you notice a change in pressure: • Increase area • Decrease area decrease pressure increase pressure • inverse relationship (opposite) p. 71

Compressible fluid (Gas) and Pressure • Particles of compressible fluid (gas) move randomly in all directions, if meet an obstacle they change direction • With each collision the fluid particles exert a force on the obstacle • The pressure in the gas depends on the number of collisions of the gas particles among themselves or the object.

Compressible fluid Pressure • Depends on: • # of collisions (the more colllisions = more pressure) • Factors that increase collision: • # of particles (the more particles = the more collisions, less particles = less colisions) • Temperature (speed of particles increase when temp. increase) (Higher temperature= more pressure. Lower temperature=less pressure)(same volume/same # or particels) • Volume of container (available space)

Volume and Pressure of Compressible Fluids • When the volume occupied by the gas decreases, the particles move closer together. There is less freedom of movement and more particle collisions. This causes the pressure to increase • When the volume occupied by the gas increases, the particles move farther apart. There is more freedom of movement and fewer particle collisions. This causes a decrease in pressure.

Particle theory to explain pressure (Example): • A tire pumped with air has a force exerted upon it by the particles “bouncing off” the “walls” inside the tire. • Air molecules in tire have lots of energy and hit walls. • Adding more air increases the number of molecules pushing outward = more pressure, particles collide more frequently and move close together. harder tire, volume of gas decreases. • A tire looses air because the air particles are small enough to pass through the spaces of the tire. This is called Diffusion. • As the number of molecules inside the tire decreases. There is less pressure being applied to the walls inside the tire because there are less particles and less collisions pushing against the walls. Gas particles move far apart therefore the volume of gas increases.

Compressible Fluids and Volume • If the volume increases, the pressure decreases • If the volume decreases, the pressure increases • If the pressure increases, the volume decreases • If the pressure decreases, the volume increases

Pressure exerted by incompressible fluids (liquids) • The more fluid above an object, the greater force exerted by the fluid and the greater pressure • The denser the fluid the greater the pressure • Summary: pressure exerted by an object by incompressible fluid depends on: • Depth of liquid above the object • Density of liquid

In the body: • In the body, fluids exert pressure on blood vessels (arterial pressure) • The pressure difference causes fluids to move (from high pressure to low pressure) • Lungs – air moves into lung

Atmospheric Pressure • When you suck on the straw, you're drawing all the air from the inside of the box; this air was exerting a force on the walls of the box that was equal to the pressure from the atmosphere outside the box. When you remove the air inside, you remove that force pushing out, there are no more particles pushing against the walls, so the force of the atmosphere is able to crumple to juice box. • When you suck on the straw, the air pressure in the box is reduced. The pressure of air outside the box collapses it.

Gas in soda • Gas is pressurized, when you open the can, the gas will have more space to fill and expand.