Physics: States of Matter and Fluids

States of Matter

• There are three primary states of matter: solid, liquid, and gas.
• A solid has a definite shape and volume.
• A liquid takes the shape of its container and has a definite volume.
• A gas takes the shape and volume of its container.

Fluids

• A fluid is any material that is unable to withstand a shear stress.
• Fluids respond to a shear stress with an irrecoverable flow.
• Examples of fluids include gases and liquids.

Fluid Properties - Density

• The mass density (ρ) of a substance is the mass of the substance divided by the volume it occupies.
• The density of water is 1000 kg/m3.
• Density can be used to find the mass and weight of a substance.

Fluid Properties - Pressure

• Pressure is the force exerted per unit area.
• Units of pressure include N/m2, Pascal (Pa), and pounds per square inch (psi).
• The same force applied over a smaller area results in greater pressure.
• Atmospheric pressure is due to the weight of the atmosphere above us.

Fluid Properties - Hydrostatic Pressure

• Hydrostatic pressure is the pressure exerted by a fluid at rest.
• A fluid exerts pressure in all directions and perpendicular to any surface it contacts.
• Pressure increases with depth.

Pressure vs. Depth

• The force exerted by a fluid on an object can be calculated using the formula Fwater = Fatm + mg.
• The pressure exerted by a fluid can be calculated using the formula P = Po + ρgh.
• Gauge pressure is the change in pressure or the difference between the initial and absolute pressure.

Pascal's Principle

• Pascal's Principle states that when pressure is applied to an enclosed fluid, the pressure is transmitted equally to every point in the fluid and to every point on the walls of the container.
• This principle has many applications, such as in plumbing and car brake systems.

Examples of Pascal's Principle

• Brakes: A small initial force applied to the brake pedal is transferred to a larger force applied to the brake shoes, allowing the car to slow down.
• Hydraulic Lift: Compressed air exerts a force on a small piston, which is transmitted to a larger piston, allowing a car to be lifted.

Buoyancy

• When an object is immersed in a fluid, it is buoyed upward by a force called the buoyant force.
• The buoyant force is equal to the weight of the fluid displaced.
• Archimedes' Principle states that an object is buoyed up by a force equal to the weight of the fluid displaced.

Archimedes' Principle

• The buoyant force can be calculated using the formula FB = (mg)Fluid = ρVg.
• The weight of the fluid displaced is equal to the weight of the object in air minus the weight of the object in water.